# Linux emacs command

Updated: 05/04/2019 by Computer Hope

On Unix-like operating systems, the emacs command launches Emacs, a comprehensive, customizable text editor, optimized for software development.

## Syntax

emacs [ command-line switches ] [ files ... ]

### Description

Emacs is a highly extensible, extremely customizable text editor originally written for the PDP-10 by Richard Stallman in the 1970s. It incorporates over 2000 commands, which can be extended using Emacs Lisp, and automated by user-created macros.

Emacs can do much more than simple insertion and deletion of text. It can control subprocesses, indent programs automatically, show multiple files at once, and more. Emacs editing commands operate in terms of characters, words, lines, sentences, paragraphs, and pages, as well as expressions and comments in various programming languages.

Emacs is called "self-documenting" because at any time you can use special commands, known as help commands, to find out what your options are, or to find out what any command does, or to find all the commands that pertain to a given topic.

Emacs is customizable in that you can easily alter its behavior in simple ways. For instance, if you use a programming language in which comments start with '<**' and end with '**>', you can tell the Emacs comment manipulation commands to use those strings (see Comments). To use another example, you can rebind the basic cursor motion commands (up, down, left and right) to any keys on the keyboard that you find comfortable. See Customization.

Emacs is extensible in that you can go beyond simple customization and create entirely new commands. New commands are programs written in the Lisp language, which are run by Emacs's own Lisp interpreter. Existing commands can even be redefined in the middle of an editing session, without having to restart Emacs. Most of the editing commands in Emacs are written in Lisp; the few exceptions could have been written in Lisp but use C instead for efficiency. Writing an extension is programming, but non-programmers can use it afterwards.

### Getting help from within Emacs

Emacs has an extensive built-in help facility, but it assumes that you know how to manipulate Emacs windows and buffers. Ctrl-h or F1 enters the Help facility. "Help Tutorial" (Ctrl-h t) starts an interactive tutorial which can teach beginners the fundamentals of Emacs in a few minutes. "Help Apropos" (Ctrl-h a) helps you find a command given its functionality, "Help Character" (Ctrl-h c) describes a given character's effect, and "Help Function" (Ctrl-h f) describes a given Lisp function specified by name.

This documentation covers GNU Emacs, which includes special packages to handle mail reading (RMail) and mail sending (Mail); outline editing (Outline); compiling (Compile); running sub-shells within Emacs windows (Shell); running a Lisp read-eval-print loop (Lisp-Interaction-Mode), automated psychotherapy (seriously. It's called Doctor), and much more.

## Options

General-interest Emacs options:

 file Edit file file. --file file, --find-file file, --visit file The same as specifying file directly as an argument. +number Go to the line specified by number (do not insert a space between the "+" sign and the number). This applies only to the next file specified. +line:column Go to the specified line and column -q, --no-init-file Do not load an init file. -no-site-file Do not load the site-wide startup file. --no-desktop Do not load a saved desktop. -Q, --quick Similar to "-q --no-site-file --no-spash". Also, skips any processing of X Windows resources. --no-splash Do not display a splash screen during startup. --debug-init Enable the Emacs Lisp debugger during the processing of the user init file ~/.emacs. This is useful for debugging problems in the init file. -u user, --user user Load user's init file. -t file, --terminal file Use specified file as the terminal instead of using stdin/stdout. This must be the first argument specified in the command line. --daemon Start Emacs as a daemon, enabling the Emacs server and disconnecting from the terminal. You can then use the emacsclient command to connect to the server. --version Display Emacs version information and exit. --help Display a help message and exit.

The following options are lisp-oriented (these options are processed in the order encountered):

 -f function, --funcall function Execute the lisp function function. -l file, --load file Load the lisp code in the file file. -eval expr, --execute expr Evaluate the Lisp expression expr.

The following options are useful when running Emacs as a batch editor:

 --batch Edit in batch mode. The editor will send messages to standard error. You must use -l and -f options to specify files to execute and functions to call. --script file Run file as an Emacs lisp script. --insert file Insert contents of file into the current buffer. --kill Exit Emacs while in batch mode. -L directory, --directory directory Add directory to the list of directories where Emacs searches for Lisp files.

### Using Emacs with X

Emacs is designed to work well with the X Window system. If you run Emacs under X Windows, it will create its own window to be displayed. You will probably want to run it as a background process so that you can still use your original window. Emacs can be started with the following X-related switches:

 --name name Specify the name which should be assigned to the initial Emacs window. This controls looking up X resources as well as the title of the window. -T name, --title name Specify the title for the initial X window. -r, -rv, --reverse-video Display the Emacs window in reverse video. -fn font, --font font Set the Emacs window's font to that specified by font. You will find the various X fonts in the /usr/lib/X11/fonts directory. Note that Emacs will only accept fixed width fonts. Under the X11 Release 4 font-naming conventions, any font with the value "m" or "c" in the eleventh field of the font name is a fixed width font. Fonts whose name are of the form widthxheight are generally fixed width, as is the font fixed. --xrm resources Set additional X resources. --color, --color=mode Override color mode for character terminals; mode defaults to auto', and can also be never', auto', always', or a mode name like ansi8'. -bw pixels, --border-width pixels Set the Emacs window's border width to the number of pixels specified by pixels. Defaults to one pixel on each side of the window. -ib pixels, --internal-border pixels Set the window's internal border width to the number of pixels specified by pixels. Defaults to one pixel of padding on each side of the window. -g geometry, --geometry geometry Set the Emacs window's width, height, and position as specified. The geometry specification is in the standard X format; see X(7) for more information. The width and height are specified in characters; the default is 80 by 24. See the Emacs manual, section "Options for Window Size and Position", for information on how window sizes interact with selecting or deselecting the tool bar and menu bar. -lsp pixels, --line-spacing pixels Additional space to put between lines. -vb, --vertical-scroll-bars Enable vertical scrollbars. -fh, --fullheight Make the first frame as high as the screen. -fs, --fullscreen Make the first frame fullscreen. -fw, --fullwidth Make the first frame as wide as the screen. -mm, --maximized Maximize the first frame, like "-fw -fh". -fg color, --foreground-color color On color displays, set the color of the text. Use the command M-x list-colors-display for a list of valid color names. -bg color, --background-color color On color displays, set the color of the window's background. -bd color, --border-color color On color displays, set the color of the window's border. -cr color, --cursor-color color On color displays, set the color of the window's text cursor. -ms color, --mouse-color color On color displays, set the color of the window's mouse cursor. -d displayname, --display displayname Create the Emacs window on the display specified by displayname. Must be the first option specified in the command line. -nbi, --no-bitmap-icon Do not use picture of the GNU gnu for the Emacs icon. --iconic Start Emacs in iconified state. -nbc, --no-blinking-cursor Do not use a blinking cursor. -nw, --no-window-system Tell Emacs not to create a graphical frame. If you use this switch when invoking Emacs from an xterm window, display is done in that window. -D, --basic-display This option disables many display features; use it for debugging Emacs.

### Configuring Emacs defaults for X

You can set X default values for your Emacs windows in your .Xresources file. Use the following format:

emacs.keyword:value 

where value specifies the default value of keyword. Emacs lets you set default values for the following keywords:

 background (class Background) For color displays, sets the window's background color. bitmapIcon (class BitmapIcon) If bitmapIcon's value is set to on, the window will iconify. borderColor (class BorderColor) For color displays, sets the color of the window's border. borderWidth (class BorderWidth) Sets the window's border width in pixels. cursorColor (class Foreground) For color displays, sets the color of the window's text cursor. cursorBlink (class CursorBlink) Specifies whether to make the cursor blink. The default is on. Use off or false to turn cursor blinking off. font (class Font) Sets the window's text font. foreground (class Foreground) For color displays, sets the window's text color. fullscreen (class Fullscreen) The desired fullscreen size. The value can be one of fullboth, maximized, fullwidth, or fullheight, which correspond to the command-line options -fs', -mm', -fw', and -fh', respectively. Note that this applies to the initial frame only. geometry (class Geometry) Sets the geometry of the Emacs window (as described above). iconName (class Title) Sets the icon name for the Emacs window icon. internalBorder (class BorderWidth) Sets the window's internal border width in pixels. lineSpacing (class LineSpacing) Additional space ("leading") between lines, in pixels. menuBar (class MenuBar) Gives frames menu bars if on; don't have menu bars if off. minibuffer (class Minibuffer) If none, don't make a minibuffer in this frame. It will use a separate minibuffer frame instead. paneFont (class Font) Font name for menu pane titles, in non-toolkit versions of Emacs. pointerColor (class Foreground) For color displays, sets the color of the window's mouse cursor. privateColormap (class PrivateColormap) If on, use a private color map, in the case where it is the "default visual" of class PseudoColor and Emacs is using it. reverseVideo (class ReverseVideo) If reverseVideo's value is set to on, the window will be displayed in reverse video. screenGamma (class ScreenGamma) Gamma correction for colors, equivalent to the frame parameter screen-gamma'. scrollBarWidth (class ScrollBarWidth) The scroll bar width in pixels, equivalent to the frame parameter scroll-bar-width'. selectionFont (class SelectionFont) Font name for pop-up menu items, in non-toolkit versions of Emacs. selectionTimeout (class SelectionTimeout) Number of milliseconds to wait for a selection reply. A value of 0 means wait as long as necessary. synchronous (class Synchronous) Run Emacs in synchronous mode if on. Synchronous mode is useful for debugging X problems. title (class Title) Sets the title of the Emacs window. toolBar (class ToolBar) Number of lines to reserve for the tool bar. useXIM (class UseXIM) Turns off use of X input methods (XIM) if false or off. verticalScrollBars (class ScrollBars) Gives frames scroll bars if on; suppresses scroll bars if off. visualClass (class VisualClass) Specify the "visual" that X should use. This tells X how to handle colors. The value should start with one of TrueColor, PseudoColor, DirectColor, StaticColor, GrayScale, and StaticGray, followed by -depth, where depth is the number of color planes.

## The Organization of the Emacs Screen

On a graphical display, such as on GNU/Linux using the X Window System, Emacs occupies a "graphical window". On a text terminal, Emacs occupies the entire terminal screen. We will use the term frame to mean a graphical window or terminal screen occupied by Emacs. Emacs behaves very similarly on both kinds of frames. It normally starts out with just one frame, but you can create additional frames if you wish (see Frames).

Each frame consists of several distinct regions. At the top of the frame is a menu bar, which allows you to access commands via a series of menus. On a graphical display, directly below the menu bar is a tool bar, a row of icons that perform editing commands if you click on them. At the very bottom of the frame is an echo area, where informative messages are displayed and where you enter information when Emacs asks for it.

The main area of the frame, below the tool bar (if one exists) and above the echo area, is called the window. Graphical display systems commonly use the word "window" with a different meaning; but here we refer to those "graphical windows" as "frames".

An Emacs window is where the buffer (the text you are editing) is displayed. On a graphical display, the window possesses a scroll bar on one side, which can be used to scroll through the buffer. The last line of the window is a mode line. This displays various information about what is going on in the buffer, such as whether there are unsaved changes, the editing modes that are in use, the current line number, and so forth.

When you start Emacs, there is normally only one window in the frame. However, you can subdivide this window horizontally or vertically to create multiple windows, each of which can independently display a buffer (see Windows).

At any time, one window is the selected window. On a graphical display, the selected window shows a more prominent cursor (usually solid and blinking); other windows show a less prominent cursor (usually a hollow box). On a text terminal, there is only one cursor, which is shown in the selected window. The buffer displayed in the selected window is called the current buffer, and it is where editing happens. Most Emacs commands implicitly apply to the current buffer; the text displayed in unselected windows is mostly visible for reference. If you use multiple frames on a graphical display, selecting a particular frame selects a window in that frame.

• Point: The place in the text where editing commands operate.
• Echo Area: Short messages appear at the bottom of the screen.
• Mode Line: Interpreting the mode line.

## Point

The cursor in the selected window shows the location where most editing commands take effect, which is called point. Many Emacs commands move point to different places in the buffer; for example, you can place point by clicking mouse button 1 (normally the left button) at the desired location.

By default, the cursor in the selected window is drawn as a solid block and appears to be on a character, but you should think of point as between two characters; it is situated before the character under the cursor. For example, if your text looks like 'frob' with the cursor over the 'b', then point is between the 'o' and the 'b'. If you insert the character '!' at that position, the result is 'fro!b', with point between the '!' and the 'b'. Thus, the cursor remains over the 'b', as before.

If you are editing several files in Emacs, each in its own buffer, each buffer has its own value of point. A buffer that is not currently displayed remembers its value of point if you later display it again. Furthermore, if a buffer is displayed in multiple windows, each of those windows has its own value of point.

See Cursor Display, for options that control how Emacs displays the cursor.

## The Echo Area

The line at the very bottom of the frame is the echo area. It is used to display small amounts of text for various purposes.

The echo area is so-named because one of the things it is used for is echoing, which means displaying the characters of a multi-character command as you type. Single-character commands are not echoed. Multi-character commands (see Keys) are echoed if you pause for more than a second in the middle of a command. Emacs then echoes all the characters of the command so far, to prompt you for the rest. Once echoing has started, the rest of the command echoes immediately as you type it. This behavior is designed to give confident users fast response, while giving hesitant users maximum feedback.

The echo area is also used to display an error message when a command cannot do its job. Error messages may be accompanied by beeping or by flashing the screen.

Some commands display informative messages in the echo area to tell you what the command has done, or to provide you with some specific information. These informative messages, unlike error messages, are not accompanied with a beep or flash. For example, C-x means the following: hold down Ctrl and type x, then let go of Ctrl and type =. This displays a message describing the character at point, its position in the buffer, and its current column in the window. Commands that take a long time often display messages ending in '...' while they are working (sometimes also indicating how much progress has been made, as a percentage), and add 'done' when they are finished.

Informative echo area messages are saved in a special buffer named *Messages*. Buffers have not been explained yet; see Buffers for more information about them. If you miss a message that appeared briefly on the screen, you can switch to the *Messages* buffer to see it again. The *Messages* buffer is limited to a certain number of lines, specified by the variable message-log-max. See Variables for more information about them. Beyond this limit, one line is deleted from the beginning whenever a new message line is added at the end.

See Display Custom for options that control how Emacs uses the echo area.

The echo area is also used to display the minibuffer, a special window where you can input arguments to commands, such as the name of a file to be edited. When the minibuffer is in use, the text displayed in the echo area begins with a prompt string, and the active cursor appears within the minibuffer, which is temporarily considered the selected window. You can always get out of the minibuffer by typing C-g. See Minibuffer for more info.

## The Mode Line

At the bottom of each window is a mode line, which describes what is going on in the current buffer. When there is only one window, the mode line appears right above the echo area; it is the next-to-last line in the frame. On a graphical display, the mode line is drawn with a 3D box appearance. Emacs also usually draws the mode line of the selected window with a different color than that of unselected windows, to make it stand out.

The text displayed in the mode line has the following format:

cs:ch-fr buf pos line (major minor) 

On a text terminal, this text is followed by a series of dashes extending to the right edge of the window. These dashes are omitted on a graphical display.

The cs string and the colon character after it describe the character set and newline convention used for the current buffer. Normally, Emacs automatically handles these settings for you, but it is sometimes useful to have this information.

cs describes the character set of the text in the buffer (see Coding Systems). If it is a dash ('-'), that indicates no special character set handling (with the possible exception of end-of-line conventions, described in the next paragraph). '=' means no conversion whatsoever, and is usually used for files containing non-textual data. Other characters represent various coding systems—for example, '1' represents ISO Latin-1.

On a text terminal, cs is preceded by two additional characters that describe the coding systems for keyboard input and terminal output. If you are using an input method, cs is preceded by a string that identifies the input method (see Input Methods).

The character after cs is usually a colon. If a different string is displayed, that indicates a nontrivial end-of-line convention for encoding a file. Usually, lines of text are separated by newline characters in a file, but two other conventions are sometimes used. The MS-DOS convention uses a "carriage-return" character followed by a "linefeed" character; when editing such files, the colon changes to either a backslash ('\') or '(DOS)', depending on the operating system. Another convention, employed by older Macintosh systems, uses a "carriage-return" character instead of a newline; when editing such files, the colon changes to either a forward slash ('/') or '(Mac)'. On some systems, Emacs displays '(Unix)' instead of the colon for files that use newline as the line separator.

The next element on the mode line is the string indicated by ch. This shows two dashes ('--') if the buffer displayed in the window has the same contents as the corresponding file on the disk; i.e., if the buffer is "unmodified". If the buffer is modified, it shows two stars ('**'). For a read-only buffer, it shows '%*' if the buffer is modified, and '%%' otherwise.

The character after ch is normally a dash ('-'). However, if the default-directory for the current buffer is on a remote machine, '@' is displayed instead (see File Names).

fr gives the selected frame name (see Frames). It appears only on text terminals. The initial frame's name is 'F1'.

buf is the name of the buffer displayed in the window. Usually, this is the same as the name of a file you are editing. See Buffers.

pos tells you whether there is additional text above the top of the window, or below the bottom. If your buffer is small and all of it is visible in the window, pos is 'All'. Otherwise, it is 'Top' if you are looking at the beginning of the buffer, 'Bot' if you are looking at the end of the buffer, or 'nn%', where nn is the percentage of the buffer above the top of the window. With Size Indication mode, you can display the size of the buffer as well. See Optional Mode Line.

line is the character 'L' followed by the line number at point. You can display the current column number too, by turning on Column Number mode. See Optional Mode Line.

major is the name of the major mode used in the buffer. A major mode is a principal editing mode for the buffer, such as Text mode, Lisp mode, C mode, and so forth. See Major Modes. Some major modes display additional information after the major mode name. For example, Compilation buffers and Shell buffers display the status of the subprocess.

minor is a list of some of the enabled minor modes, which are optional editing modes that provide additional features on top of the major mode. See Minor Modes.

Some features are listed together with the minor modes whenever they are turned on, even though they are not really minor modes. 'Narrow' means that the buffer being displayed has editing restricted to only a portion of its text (see Narrowing). 'Def' means that a keyboard macro is currently being defined (see Keyboard Macros).

Also, if Emacs is inside a recursive editing level, square brackets ('[...]') appear around the parentheses that surround the modes. If Emacs is in one recursive editing level within another, double square brackets appear, and so on. Since recursive editing levels affect Emacs globally, such square brackets appear in the mode line of every window. See Recursive Edit.

You can change the appearance of the mode line as well as the format of its contents; see Optional Mode Line. Also, the mode line is mouse-sensitive; clicking on different parts of the mode line performs various commands. See Mode Line Mouse.

Each Emacs normally has a menu bar at the top which you can use to perform common operations. There's no need to list them here, as you can more easily see them yourself.

On a graphical display, you can use the mouse to choose a command from the menu bar. An arrow on the right edge of a menu item means it leads to a subsidiary menu, or "submenu". A '...' at the end of a menu item means that the command will prompt you for further input before it actually does anything.

Some of the commands in the menu bar have ordinary key bindings as well; if so, a key binding is shown in parentheses after the item itself. To view the full command name and documentation for a menu item, type C-h k, and then select the menu bar with the mouse in the usual way (see Key Help).

Kinds of User Input

Keyboard input in Emacs is based on a heavily-extended version of ASCII. Simple characters, like 'a', 'B', '3', '=', and the space character (denoted as <SPC>), are entered by typing the corresponding key. Control characters, such as <RET>, <TAB>, <DEL>, <ESC>, <F1>, <Home>, and <left>, are also entered this way, as are certain characters found on non-English keyboards (see International).

Emacs also recognizes control characters that are entered using modifier keys. Two commonly-used modifier keys are Control (usually labeled Ctrl), and Meta (usually labeled Alt). For example, Control-a is entered by holding down the Ctrl key while pressing a; this is referred to this as C-a for short. Similarly Meta-a, or M-a for short, is entered by holding down the Alt key and pressing a. Modifier keys can also be applied to non-alphanumerical characters, e.g., C-F1 or M-left.

You can also type Meta characters using two-character sequences starting with <ESC>. Thus, you can enter M-a by typing <ESC> a. You can enter C-M-a by typing <ESC> C-a. Unlike Meta, <ESC> is entered as a separate character. You don't hold down <ESC> while typing the next character; instead, press <ESC> and release it, then enter the next character. This feature is useful on certain text terminals where the Meta key does not function reliably.

On graphical displays, the window manager might block some keyboard inputs, including M-<TAB>, M-<SPC>, C-M-d and C-M-l. If you have this problem, you can either customize your window manager to not block those keys, or "rebind" the affected Emacs commands (see Customization).

Simple characters and control characters, as well as certain non-keyboard inputs such as mouse clicks, are collectively referred to as input events.

## Keys

Some Emacs commands are invoked by just one input event; for example, C-f moves forward one character in the buffer. Other commands take two or more input events to invoke, such as C-x C-f and C-x 4 C-f.

A key sequence, or key for short, is a sequence of one or more input events that is meaningful as a unit. If a key sequence invokes a command, we call it a complete key; for example, C-f, C-x C-f and C-x 4 C-f are all complete keys. If a key sequence isn't long enough to invoke a command, we call it a prefix key; from the preceding example, we see that C-x and C-x 4 are prefix keys. Every key sequence is either a complete key or a prefix key.

A prefix key combines with the following input event to make a longer key sequence. For example, C-x is a prefix key, so typing C-x alone does not invoke a command; instead, Emacs waits for further input (if you pause for longer than a second, it echoes the C-x key to prompt for that input; see Echo Area). C-x combines with the next input event to make a two-event key sequence, which could itself be a prefix key (such as C-x 4), or a complete key (such as C-x C-f). There is no limit to the length of key sequences, but in practice they are seldom longer than three or four input events.

You can't add input events onto a complete key. For example, because C-f is a complete key, the two-event sequence C-f C-k is two key sequences, not one.

By default, the prefix keys in Emacs are C-c, C-h, C-x, C-x <RET>, C-x @, C-x a, C-x n, C-x r, C-x v, C-x 4, C-x 5, C-x 6, <ESC>, M-g, and M-o. (F1 and F2 are aliases for C-h and C-x 6.) This list is not cast in stone; if you customize Emacs, you can make new prefix keys. You could even eliminate some of the standard ones, though this is not recommended for most users; for example, if you remove the prefix definition of C-x 4, then C-x 4 C-f becomes an invalid key sequence. See Key Bindings. Typing the help character (C-h or F1) after a prefix key displays a list of the commands starting with that prefix. The sole exception to this rule is <ESC>: <ESC> C-h is equivalent to C-M-h, which does something else entirely. You can, however, use F1 to display a list of commands starting with <ESC>.

## Keys and Commands

Emacs does not assign meanings to keys directly. Instead, Emacs assigns meanings to named commands, and then gives keys their meanings by binding them to commands.

Every command has a name chosen by a programmer. The name is usually made of a few English words separated by dashes; for example, next-line or forward-word. Internally, each command is a special type of Lisp function, and the actions associated with the command are performed by running the function.

The bindings between keys and commands are recorded in tables called keymaps. See Keymaps. The description "C-n moves down vertically one line" glosses over a subtle distinction that is irrelevant in ordinary use, but vital for Emacs customization. The command next-line does a vertical move downward. C-n has this effect because it is bound to next-line. If you rebind C-n to the command forward-word, C-n will move forward one word instead.

In this manual, we will often speak of keys like C-n as commands, even though strictly speaking the key is bound to a command. Usually we state the name of the command which really does the work in parentheses after mentioning the key that runs it. For example, we will say that "The command C-n (next-line) moves point vertically down", meaning that the command next-line moves vertically down, and the key C-n is normally bound to it. Since we are discussing customization, we should tell you about variables. Often the description of a command will say, "To change this, set the variable this-that." A variable is a name used to store a value. Most of the variables documented in this manual are meant for customization: some command or other part of Emacs examines the variable and behaves differently according to the value that you set. You can ignore the information about variables until you are interested in customizing them. Then read the basic information on variables (see Variables) and the information about specific variables will make sense.

## Entering Emacs

The usual way to invoke Emacs is with the shell command emacs. From a terminal window running in the X Window System, you can run Emacs in the background with emacs &; this way, Emacs won't tie up the terminal window, so you can use it to run other shell commands.

When Emacs starts up, the initial frame displays a special buffer named '*GNU Emacs*'. This startup screen contains information about Emacs and links to common tasks that are useful for beginning users. For instance, activating the 'Emacs Tutorial' link opens the Emacs tutorial; this does the same thing as the command C-h t (help-with-tutorial). To activate a link, either move point onto it and type <RET>, or click on it with mouse-1 (the left mouse button).

Using a command line argument, you can tell Emacs to visit one or more files as soon as it starts up. For example, emacs foo.txt starts Emacs with a buffer displaying the contents of the file 'foo.txt'. This feature exists mainly for compatibility with other editors, which are designed to be launched from the shell for short editing sessions. If you call Emacs this way, the initial frame is split into two windows: one showing the specified file, and the other showing the startup screen. See Windows.

Generally, it is unnecessary and wasteful to start Emacs afresh each time you want to edit a file. The recommended way to use Emacs is to start it just once, just after you log in, and do all your editing in the same Emacs session. See Files, for information on visiting more than one file. If you use Emacs this way, the Emacs session accumulates valuable context, such as the kill ring, registers, undo history, and mark ring data, which together make editing more convenient. These features are described later in the manual.

To edit a file from another program while Emacs is running, you can use the emacsclient helper program to open a file in the existing Emacs session. See Emacs Server.

Emacs accepts other command line arguments that tell it to load certain Lisp files, where to put the initial frame, and so forth. See Emacs Invocation.

If the variable inhibit-startup-screen is set to anything, Emacs does not display the startup screen. In that case, if one or more files were specified on the command line, Emacs displays those files; otherwise, it displays a buffer named *scratch*, which can be used to evaluate Emacs Lisp expressions interactively. See Lisp Interaction. You can set the variable inhibit-startup-screen using the Customize facility (see Easy Customization), or by editing your initialization file (see Init File).

You can also force Emacs to display a file or directory at startup by setting the variable initial-buffer-choice to a value. In that case, even if you specify one or more files on the command line, Emacs opens but does not display them. The value of initial-buffer-choice should be the name of the desired file or directory.

## Exiting Emacs

C-x C-c

Kills Emacs (save-buffers-kill-terminal).

C-z

On a text terminal, this suspends Emacs; on a graphical display, "minimize" the selected frame (suspend-emacs).

Killing Emacs means terminating the Emacs program. To do this, type C-x C-c (save-buffers-kill-terminal). A two-character key sequence is used to make it harder to type by accident. If there are any modified file-visiting buffers when you type C-x C-c, Emacs first offers to save these buffers. If you do not save them all, it asks for confirmation again, since the unsaved changes will be lost. Emacs also asks for confirmation if any subprocesses are still running, since killing Emacs will also kill the subprocesses (see Shell).

C-x C-c behaves specially if you are using Emacs as a server. If you type it from a "client frame", it closes the client connection. See Emacs Server.

Emacs can, optionally, record certain session information when you kill it, such as the files you were visiting at the time. This information is then available the next time you start Emacs. See Saving Emacs Sessions. If the value of the variable confirm-kill-emacs is non-nil, C-x C-c assumes that its value is a predicate function, and calls that function. If the result of the function call is not nil, the session is killed, otherwise Emacs continues to run. One convenient function to use as the value of confirm-kill-emacs is the function yes-or-no-p. The default value of confirm-kill-emacs is nil.

To kill Emacs without being prompted about saving, type M-x kill-emacs.

C-z runs the command suspend-frame. On a graphical display, this command minimizes (or iconifies) the selected Emacs frame, hiding it in a way that lets you bring it back later (exactly how this hiding occurs depends on the window system). On a text terminal, the C-z command suspends Emacs, stopping the program temporarily and returning control to the parent process (usually a shell); in most shells, you can resume Emacs after suspending it with the shell command %emacs.

Text terminals usually listen for certain special characters whose meaning is to kill or suspend the program you are running. This terminal feature is turned off while you are in Emacs. The meanings of C-z and C-x C-c as keys in Emacs were inspired by the use of C-z and C-c on several operating systems as the characters for stopping or killing a program, but that is their only relationship with the operating system. You can customize these keys to run any commands of your choice (see Keymaps).

## Basic Editing Commands

The following sections explain the basics of how to enter text, make corrections, and save the text in a file. If this material is new to you, it's suggested you first run the Emacs learn-by-doing tutorial, by typing C-h t (help-with-tutorial).

• Inserting Text: Inserting text by typing it.
• Moving Point: Moving the cursor to the place where you want to change something.
• Erasing: Deleting and killing text.
• Basic Undo: Undoing recent changes in the text.
• Files: Visiting, creating, and saving files.
• Help: Asking what a character does.
• Blank Lines: Making and deleting blank lines.
• Continuation Lines: How Emacs displays lines too wide for the screen.
• Position Info: What line, row, or column is point on?
• Arguments: Numeric arguments for repeating a command N times.
• Repeating: Repeating the previous command quickly.

## Inserting Text

You can insert an ordinary graphic character (e.g., 'a', 'B', '3', and '=') by typing the associated key. This adds the character to the buffer at point. Insertion moves point forward, so that point remains just after the inserted text. See Point.

To end a line and start a new one, type <RET> (newline). The <RET> key may be labeled Return or Enter on your keyboard, but Emacs refers to it as <RET>. This command inserts a newline character into the buffer. If point is at the end of the line, the effect is to create a new blank line after it; if point is in the middle of a line, the line is split at that position.

You can change the way Emacs handles text insertion by turning on minor modes. For instance, the minor mode called Auto Fill mode splits lines automatically when they get too long (see Filling). The minor mode called Overwrite mode causes inserted characters to replace (overwrite) existing text, instead of shoving it to the right. See Minor Modes.

Only graphic characters can be inserted by typing the associated key; other keys act as editing commands and do not insert themselves. For instance, <DEL> runs the command delete-backward-char by default (some modes bind it to a different command); it does not insert a literal '<DEL>' character (ASCII character code 127).

To insert a non-graphic character, or a character that your keyboard does not support, first quote it by typing C-q (quoted-insert). There are two ways to use C-q:

• C-q followed by any non-graphic character (even C-g) inserts that character. For instance, C-q <DEL> inserts a literal '<DEL>' character.
• C-q followed by a sequence of octal digits inserts the character with the specified octal character code. You can use any number of octal digits; any non-digit terminates the sequence. If the terminating character is <RET>, that <RET> serves only to terminate the sequence. Any other non-digit terminates the sequence and then acts as normal input; thus, C-q 1 0 1 B inserts 'AB'. The use of octal sequences is disabled in ordinary non-binary Overwrite mode, to give you a convenient way to insert a digit instead of overwriting with it.

To use decimal or hexadecimal instead of octal, set the variable read-quoted-char-radix to 10 or 16. If the radix is 16, the letters a to f serve as part of a character code, just like digits. Case is ignored.

Alternatively, you can use the command C-x 8 <RET> (insert-char). This prompts for the Unicode name or code-point of a character, using the minibuffer. If you enter a name, the command provides completion (see Completion). If you enter a code-point, it should be as a hexadecimal number (the convention for Unicode), or a number with a specified radix, e.g., #o23072 (octal). The command then inserts the corresponding character into the buffer. For example, both of the following insert the infinity sign (Unicode code-point U+221E):

• C-x 8 <RET> infinity <RET>
• C-x 8 <RET> 221e <RET>

A numeric argument to C-q or C-x 8 <RET> specifies how many copies of the character to insert (see Arguments).

## Changing the Location of Point

To do more than insert characters, you have to know how to move point (see Point). The keyboard commands C-f, C-b, C-n, and C-p move point to the right, left, down, and up, respectively. You can also move point using the arrow keys; however, many Emacs users find that it is slower to use the arrow keys than the control keys, because you need to move your hand to the area of the keyboard where those keys are located.

You can also click the left mouse button to move point to the position clicked. Emacs also provides a variety of additional keyboard commands that move point in more sophisticated ways.

 C-f Move forward one character (forward-char). This command (right-char) behaves like C-f, with one exception: when editing right-to-left scripts such as Arabic, it instead moves backward if the current paragraph is a right-to-left paragraph. See Bidirectional Editing. C-b Move backward one character (backward-char). This command (left-char) behaves like C-b, except it moves forward if the current paragraph is right-to-left. See Bidirectional Editing. C-n, Move down one screen line (next-line). This command attempts to keep the horizontal position unchanged, so if you start in the middle of one line, you move to the middle of the next. C-p, Move up one screen line (previous-line). This command preserves position within the line, like C-n. C-a, Move to the beginning of the line (move-beginning-of-line). C-e, Move to the end of the line (move-end-of-line). M-f Move forward one word (forward-word). C-, M- This command (right-word) behaves like M-f, except it moves backward by one word if the current paragraph is right-to-left. See Bidirectional Editing. M-b Move backward one word (backward-word). C-, M- This command (left-word) behaves like M-f, except it moves forward by one word if the current paragraph is right-to-left. See Bidirectional Editing. M-r Without moving the text on the screen, reposition point on the left margin of the center-most text line of the window; on subsequent consecutive invocations, move point to the left margin of the top-most line, the bottom-most line, and so forth, in cyclic order (move-to-window-line-top-bottom). A numeric argument says which screen line to place point on, counting downward from the top of the window (zero means the top line). A negative argument counts lines up from the bottom (−1 means the bottom line). See Arguments, for more information on numeric arguments. M-< Move to the top of the buffer (beginning-of-buffer). With numeric argument n, move to n/10 of the way from the top. M-> Move to the end of the buffer (end-of-buffer). C-v, , Scroll the display one screen forward, and move point onscreen if necessary (scroll-up-command). See Scrolling. M-v, , Scroll one screen backward, and move point onscreen if necessary (scroll-down-command). See Scrolling. M-g c Read a number n and move point to buffer position n. Position 1 is the beginning of the buffer. M-g M-g, M-g g Read a number n and move point to the beginning of line number n (goto-line). Line 1 is the beginning of the buffer. If point is on or just after a number in the buffer, that is the default for n. Just type in the minibuffer to use it. You can also specify n by giving M-g M-g a numeric prefix argument. See Select Buffer, for the behavior of M-g M-g when you give it a plain prefix argument. M-g Read a number n and move to column n in the current line. Column 0 is the leftmost column. If called with a prefix argument, move to the column number specified by the argument's numeric value. C-x C-n Use the current column of point as the semipermanent goal column for C-n and C-p (set-goal-column). When a semipermanent goal column is in effect, those commands always try to move to this column, or as close as possible to it, after moving vertically. The goal column remains in effect until canceled. C-u C-x C-n Cancel the goal column. Henceforth, C-n and C-p try to preserve the horizontal position, as usual.

When a line of text in the buffer is longer than the width of the window, Emacs usually displays it on two or more screen lines. For convenience, C-n and C-p move point by screen lines, as do the equivalent keys down and up. You can force these commands to move according to logical lines (i.e., according to the text lines in the buffer) by setting the variable line-move-visual to nil; if a logical line occupies multiple screen lines, the cursor then skips over the additional screen lines. For details, see Continuation Lines. See Variables, for how to set variables such as line-move-visual.

Unlike C-n and C-p, most of the Emacs commands that work on lines work on logical lines. For instance, C-a (move-beginning-of-line) and C-e (move-end-of-line) respectively move to the beginning and end of the logical line. Whenever we encounter commands that work on-screen lines, such as C-n and C-p, we will point these out.

When line-move-visual is nil, you can also set the variable track-eol to a non-nil value. Then C-n and C-p, when starting at the end of the logical line, move to the end of the next logical line. Normally, track-eol is nil.

C-n normally stops at the end of the buffer when you use it on the last line in the buffer. However, if you set the variable next-line-add-newlines to a non-nil value, C-n on the last line of a buffer creates an additional line at the end and moves down into it.

## Erasing Text

 , Delete the character before point, or the region if it is active (delete-backward-char). Delete the character after point, or the region if it is active (delete-forward-char). C-d Delete the character after point (delete-char). C-k Kill to the end of the line (kill-line). M-d Kill forward to the end of the next word (kill-word). M- Kill back to the beginning of the previous word (backward-kill-word).

The <DEL> (delete-backward-char) command removes the character before point, moving the cursor and the characters after it backwards. If point was at the beginning of a line, this deletes the preceding newline, joining this line to the previous one.

If, however, the region is active, <DEL> instead deletes the text in the region. See Mark, for a description of the region.

On most keyboards, <DEL> is labeled Backspace, but it is referred to as <DEL> in this manual. Do not confuse <DEL> with the Delete key; Delete will be discussed momentarily. On some text terminals, Emacs may not recognize the <DEL> key properly.

The delete (delete-forward-char) command deletes in the "opposite direction": it deletes the character after point, i.e., the character under the cursor. If point was at the end of a line, this joins the following line onto this one. Like <DEL>, it deletes the text in the region if the region is active (see Mark).

C-d (delete-char) deletes the character after point, similar to delete, but regardless of whether the region is active.

See Deletion, for more detailed information about the above deletion commands.

C-k (kill-line) erases ("kills") a line at a time. If you type C-k at the beginning or middle of a line, it kills all the text up to the end of the line. If you type C-k at the end of a line, it joins that line with the following line. See Killing, for more information about C-k and related commands.

## Undoing Changes

 C-/ Undo one entry of the undo records—usually, one command worth (undo). C-x u, C-_ The same.

Emacs records a list of changes made in the buffer text, so you can undo recent changes. This is done using the undo command, which is bound to C-/ (as well as C-x u and C-_). Normally, this command undoes the last change, moving point back to where it was before the change. The undo command applies only to changes in the buffer; you can't use it to undo cursor motion.

Although each editing command usually makes a separate entry in the undo records, very simple commands may be grouped together. Sometimes, an entry may cover just part of a complex command.

If you repeat C-/ (or its aliases), each repetition undoes another, earlier change, back to the limit of the undo information available. If all recorded changes have already been undone, the undo command displays an error message and does nothing.

## Files

Text that you insert in an Emacs buffer lasts only as long as the Emacs session. To keep any text permanently, you must put it in a file.

Suppose there is a file named test.emacs in your home directory. To begin editing this file in Emacs, type

C-x C-f test.emacs <RET>

Here the file name is given as an argument to the command C-x C-f (find-file). That command uses the minibuffer to read the argument, and you type <RET> (press the Return/Enter key) to terminate the argument. See Minibuffer for more information on the minibuffer.

Emacs obeys this command by visiting the file: it creates a buffer, copies the contents of the file into the buffer, and then displays the buffer for editing. If you alter the text, you can save the new text in the file by typing C-x C-s (save-buffer). This copies the altered buffer contents back into the file test.emacs, making them permanent. Until you save, the changed text exists only inside Emacs, and the file test.emacs is unaltered.

To create a file, just visit it with C-x C-f as if it already existed. This creates an empty buffer, in which you can insert the text you want to put in the file. Emacs actually creates the file the first time you save this buffer with C-x C-s.

## Help

If you forget what a key does, you can find out by typing C-h k (describe-key), followed by the key of interest; for example, C-h k C-n tells you what C-n does.

The prefix key C-h stands for "help". The key F1 serves as an alias for C-h. Apart from C-h k, there are other help commands providing different kinds of help.

## Blank Lines

Here are special commands and techniques for inserting and deleting blank lines:

 C-o Insert a blank line after the cursor (open-line). C-x C-o Delete all but one of many consecutive blank lines (delete-blank-lines).

We have seen how <RET> (newline) starts a new line of text. However, it may be easier to see what you are doing if you first make a blank line and then insert the desired text into it. This is easy to do using the key C-o (open-line), which inserts a newline after point but leaves point in front of the newline. After C-o, type the text for the new line.

You can make several blank lines by typing C-o several times, or by giving it a numeric argument specifying how many blank lines to make. See Arguments, for how. If you have a fill prefix, the C-o command inserts the fill prefix on the new line, if typed at the beginning of a line. See Fill Prefix.

The easy way to get rid of extra blank lines is with the command C-x C-o (delete-blank-lines). If point lies within a run of several blank lines, C-x C-o deletes all but one of them. If point is on a single blank line, C-x C-o deletes it. If point is on a nonblank line, C-x C-o deletes all following blank lines, if any exists.

## Continuation Lines

Sometimes, a line of text in the buffer (a logical line) is too long to fit in the window, and Emacs displays it as two or more screen lines. This is called line wrapping or continuation, and the long logical line is called a continued line. On a graphical display, Emacs indicates line wrapping with small bent arrows in the left and right window fringes. On a text terminal, Emacs indicates line wrapping by displaying a '\' character at the right margin.

Most commands that act on lines act on logical lines, not screen lines. For instance, C-k kills a logical line. As described earlier, C-n (next-line) and C-p (previous-line) are special exceptions: they move point down and up, respectively, by one screen line (see Moving Point).

## Backslash in Regular Expressions

For the most part, '\' followed by any character matches only that character. However, there are several exceptions: two-character sequences starting with '\' that have special meanings. The second character in the sequence is always an ordinary character when used on its own. Here is a table of '\' constructs.

 \| specifies an alternative. Two regular expressions a and b with '\|' in between form an expression that matches some text if either a matches it or b matches it. It works by trying to match a, and if that fails, by trying to match b. Thus, 'foo\|bar' matches either 'foo' or 'bar' but no other string. '\|' applies to the largest possible surrounding expressions. Only a surrounding '$$...$$' grouping can limit the grouping power of '\|'. Full backtracking capability exists to handle multiple uses of '\|'. $$...$$ is a grouping construct that serves three purposes: 1. To enclose a set of '\|' alternatives for other operations. Thus, '$$foo\|bar$$x' matches either 'foox' or 'barx'. 2. To enclose a complicated expression for the postfix operators '*', '+' and '?' to operate on. Thus, 'ba$$na$$*' matches 'bananana', etc., with any (zero or more) number of 'na' strings. 3. To record a matched substring for future reference. This last application is not a consequence of the idea of a parenthetical grouping; it is a separate feature that is assigned as a second meaning to the same '$$...$$' construct. In practice there is usually no conflict between the two meanings; when there is a conflict, you can use a "shy" group. $$?: ...$$ specifies a "shy" group that does not record the matched substring; you can't refer back to it with '\d'. This is useful in mechanically combining regular expressions, so that you can add groups for syntactic purposes without interfering with the numbering of the groups that are meant to be referred to. \d matches the same text that matched the dth occurrence of a '$$...$$' construct. This is called a back reference. After the end of a '$$...$$' construct, the matcher remembers the beginning and end of the text matched by that construct. Then, later on in the regular expression, you can use '\' followed by the digit d to mean "match the same text matched the dth time by the '$$...$$' construct". The strings matching the first nine '$$...$$' constructs appearing in a regular expression are assigned numbers 1 through 9 in the order that the open-parentheses appear in the regular expression. So you can use '\1' through '\9' to refer to the text matched by the corresponding '$$...$$' constructs. For example, '$$.*$$\1' matches any newline-free string that is composed of two identical halves. The '$$.*$$' matches the first half, which may be anything, but the '\1' that follows must match the same exact text. If a particular '$$...$$' construct matches more than once (which can easily happen if it is followed by '*'), only the last match is recorded. \ matches the empty string, but only at the beginning of the string or buffer (or its accessible portion) being matched against. \' matches the empty string, but only at the end of the string or buffer (or its accessible portion) being matched against. \= matches the empty string, but only at point. \b matches the empty string, but only at the beginning or end of a word. Thus, '\bfoo\b' matches any occurrence of 'foo' as a separate word. '\bballs?\b' matches 'ball' or 'balls' as a separate word. '\b' matches at the beginning or end of the buffer regardless of what text appears next to it. \B matches the empty string, but not at the beginning or end of a word. \< matches the empty string, but only at the beginning of a word. '\<' matches at the beginning of the buffer only if a word-constituent character follows. \> matches the empty string, but only at the end of a word. '\>' matches at the end of the buffer only if the contents end with a word-constituent character. \w matches any word-constituent character. The syntax table determines which characters these are. See Syntax Tables. \W matches any character that is not a word-constituent. \_< matches the empty string, but only at the beginning of a symbol. A symbol is a sequence of one or more symbol-constituent characters. A symbol-constituent character is a character whose syntax is either 'w' or '_'. '\_<' matches at the beginning of the buffer only if a symbol-constituent character follows. \_> matches the empty string, but only at the end of a symbol. '\_>' matches at the end of the buffer only if the contents end with a symbol-constituent character. \sc matches any character whose syntax is c. Here c is a character that designates a particular syntax class: thus, 'w' for word constituent, '-' or ' ' for whitespace, '.' for ordinary punctuation, etc. \Sc matches any character whose syntax is not c. \cc matches any character that belongs to the category c. For example, '\cc' matches Chinese characters, '\cg' matches Greek characters, etc. For the description of the known categories, type M-x describe-categories . \Cc matches any character that does not belong to category c.

The constructs that pertain to words and syntax are controlled by the setting of the syntax table.

## Regular Expression Example

Here is an example of a regexp: similar to the regexp that Emacs uses, by default, to recognize the end of a sentence, not including the following space (i.e., the variable sentence-end-base):

[.?!][]\"')}]*

This contains two parts in succession: a character set matching period, '?', or '!', and a character set matching close-brackets, quotes, or parentheses, repeated zero or more times.

## Searching and Case

Searches in Emacs normally ignore the case of the text they are searching through, if you specify the text in lower case. Thus, if you specify searching for 'foo', then 'Foo' and 'foo' also match. Regexps, and in particular character sets, behave likewise: '[ab]' matches 'a' or 'A' or 'b' or 'B'.

An upper-case letter anywhere in the incremental search string makes the search case-sensitive. Thus, searching for 'Foo' does not find 'foo' or 'FOO'. This applies to regular expression search as well as to string search. The effect ceases if you delete the upper-case letter from the search string.

Typing M-c within an incremental search toggles the case sensitivity of that search. The effect does not extend beyond the current incremental search to the next one, but it does override the effect of adding or removing an upper-case letter in the current search.

If you set the variable case-fold-search to nil, then all letters must match exactly, including case. This is a per-buffer variable; altering the variable normally affects only the current buffer, unless you change its default value. See Locals. This variable applies to nonincremental searches also, including those performed by the replace commands (see Replace) and the minibuffer history matching commands (see Minibuffer History).

Several related variables control case-sensitivity of searching and matching for specific commands or activities. For instance, tags-case-fold-search controls case sensitivity for find-tag. To find these variables, do M-x apropos-variable <RET> case-fold-search <RET>.

## Replacement Commands

Emacs provides several commands for performing search-and-replace operations. In addition to the simple M-x replace-string command, there is M-% (query-replace), which presents each occurrence of the pattern and asks you whether to replace it.

The replace commands normally operate on the text from point to the end of the buffer. When the region is active, they operate on it instead (see Mark). The basic replace commands replace one search string (or regexp) with one replacement string. It is possible to perform several replacements in parallel, using the command expand-region-abbrevs (see Expanding Abbrevs).

Unlike incremental search, the replacement commands do not use lax space matching (see Special Isearch) by default. To enable lax space matching for replacement, change the variable replace-lax-whitespace to t. (This only affects how Emacs finds the text to replace, not the replacement text.)

## Unconditional Replacement

 M-x replace-string string newstring Replace every occurrence of string with newstring.

To replace every instance of 'foo' after point with 'bar', use the command M-x replace-string with the two arguments 'foo' and 'bar'. Replacement happens only in the text after point, so if you want to cover the whole buffer you must go to the beginning first. All occurrences up to the end of the buffer are replaced; to limit replacement to part of the buffer, activate the region around that part. When the region is active, replacement is limited to the region (see Mark).

When replace-string exits, it leaves point at the last occurrence replaced. It adds the prior position of point (where the replace-string command was issued) to the mark ring, without activating the mark; use C-u C-<SPC> to move back there. See Mark Ring.

A prefix argument restricts replacement to matches that are surrounded by word boundaries.

See Replacement and Case, for details about case-sensitivity in replace commands.

## Regexp Replacement

The M-x replace-string command replaces exact matches for a single string. The similar command M-x replace-regexp replaces any match for a specified pattern.

 M-x replace-regexp regexp newstring Replace every match for regexp with newstring.

In replace-regexp, the newstring need not be constant: it can refer to all or part of what is matched by the regexp. '\&' in newstring stands for the entire match being replaced. '\d' in newstring, where d is a digit, stands for whatever matched the dth parenthesized grouping in regexp. (This is called a "back reference".) '\#' refers to the count of replacements already made in this command, as a decimal number. In the first replacement, '\#' stands for '0'; in the second, for '1'; and so on. For example,

M-x replace-regexp <RET> c[ad]+r <RET> \&-safe <RET>

M-x replace-regexp <RET> $$c[ad]+r$$-safe <RET> \1 <RET>

performs the inverse transformation. To include a '\' in the text to replace with, you must enter '\\'.

If you want to enter part of the replacement string by hand each time, use '\?' in the replacement string. Each replacement will ask you to edit the replacement string in the minibuffer, putting point where the '\?' was.

The remainder of this subsection is intended for specialized tasks and requires knowledge of Lisp. Most readers can skip it.

You can use Lisp expressions to calculate parts of the replacement string. To do this, write '\,' followed by the expression in the replacement string. Each replacement calculates the value of the expression and converts it to text without quoting (if it's a string, this means using the string's contents), and uses it in the replacement string in place of the expression itself. If the expression is a symbol, one space in the replacement string after the symbol name goes with the symbol name, so the value replaces them both.

Inside such an expression, you can use some special sequences. '\&' and '\n' refer here, as usual, to the entire match as a string, and to a submatch as a string. n may be multiple digits, and the value of '\n' is nil if subexpression n did not match. You can also use '\#&' and '\#n' to refer to those matches as numbers (this is valid when the match or submatch has the form of a numeral). '\#' here too stands for the number of already-completed replacements.

Repeating our example to exchange 'x' and 'y', we can thus do it also this way:

M-x replace-regexp <RET> $$x$$\|y <RET>

\,(if \1 "y" "x") <RET>

For computing replacement strings for '\,', the format function is often useful. For example, to add consecutively numbered strings like 'ABC00042' to columns 73 to 80 (unless they are already occupied), you can use

M-x replace-regexp <RET> ^.\{0,72\}$<RET> \,(format "%-72sABC%05d" \& \#) <RET> ## Replace Commands and Case If the first argument of a replace command is all lower case, the command ignores case while searching for occurrences to replace—provided case-fold-search is non-nil. If case-fold-search is set to nil, case is always significant in all searches. Also, when the newstring argument is all or partly lower case, replacement commands try to preserve the case pattern of each occurrence. Thus, the command M-x replace-string <RET> foo <RET> bar <RET> replaces a lower case 'foo' with a lower case 'bar', an all-caps 'FOO' with 'BAR', and a capitalized 'Foo' with 'Bar'. (These three alternatives -- lower case, all caps, and capitalized -- are the only ones that replace-string can distinguish.) If upper-case letters are used in the replacement string, they remain upper case every time that text is inserted. If upper-case letters are used in the first argument, the second argument is always substituted exactly as given, with no case conversion. Likewise, if either case-replace or case-fold-search is set to nil, replacement is done without case conversion. ## Query Replace  M-% string newstring Replace some occurrences of string with newstring. C-M-% regexp newstring Replace some matches for regexp with newstring. If you want to change only some of the occurrences of 'foo' to 'bar', not all of them, use M-% (query-replace). This command finds occurrences of 'foo' one by one, displays each occurrence and asks you whether to replace it. Aside from querying, query-replace works just like replace-string (see Unconditional Replace). In particular, it preserves case provided case-replace is non-nil, as it normally is (see Replacement and Case). A numeric argument means to consider only occurrences that are bounded by word-delimiter characters. C-M-% performs regexp search and replace (query-replace-regexp). It works like replace-regexp except that it queries like query-replace. These commands highlight the current match using the face query-replace. They highlight other matches using lazy-highlight just like incremental search (see Incremental Search). By default, query-replace-regexp will show the substituted replacement string for the current match in the minibuffer. If you want to keep special sequences '\&' and '\n' unexpanded, customize query-replace-show-replacement variable. The characters you can type when you are shown a match for the string or regexp are:  to replace the occurrence with newstring. to skip to the next occurrence without replacing this one. , (Comma) to replace this occurrence and display the result. You are then asked for another input character to say what to do next. Since the replacement has already been made, and are equivalent in this situation; both move to the next occurrence. You can type C-r at this point (see below) to alter the replaced text. You can also type C-x u to undo the replacement; this exits the query-replace, so if you want to do further replacement you must use C-x to restart (see Repetition). to exit without doing any more replacements. . (Period) to replace this occurrence and then exit without searching for more occurrences. ! to replace all remaining occurrences without asking again. Y (Upper-case Y) to replace all remaining occurrences in all remaining buffers in multi-buffer replacements (like the Dired Q' command which performs query replace on selected files). It answers this question and all subsequent questions in the series with "yes", without further user interaction. N (Upper-case N) to skip to the next buffer in multi-buffer replacements without replacing remaining occurrences in the current buffer. It answers this question "no", gives up on the questions for the current buffer, and continues to the next buffer in the sequence. ^ to go back to the position of the previous occurrence (or what used to be an occurrence), in case you changed it by mistake or want to reexamine it. C-r to enter a recursive editing level, in case the occurrence needs to be edited rather than just replaced with newstring. When you are done, exit the recursive editing level with C-M-c to proceed to the next occurrence. See Recursive Edit. C-w to delete the occurrence, and then enter a recursive editing level as in C-r. Use the recursive edit to insert text to replace the deleted occurrence of string. When done, exit the recursive editing level with C-M-c to proceed to the next occurrence. e to edit the replacement string in the minibuffer. When you exit the minibuffer by typing , the minibuffer contents replace the current occurrence of the pattern. They also become the new replacement string for any further occurrences. C-l to redisplay the screen. Then you must type another character to specify what to do with this occurrence. C-h to display a message summarizing these options. Then you must type another character to specify what to do with this occurrence. Some other characters are aliases for the ones listed above: y, n and q are equivalent to <SPC>, <DEL> and <RET>. Aside from this, any other character exits the query-replace, and is then reread as part of a key sequence. Thus, if you type C-k, it exits the query-replace and then kills to end of line. To restart a query-replace once it is exited, use C-x <ESC> <ESC>, which repeats the query-replace because it used the minibuffer to read its arguments. See C-x <ESC> <ESC>. See Operating on Files, for the Dired Q command which performs query replace on selected files. See also Transforming File Names, for Dired commands to rename, copy, or link files by replacing regexp matches in file names. Here are some other commands that find matches for a regular expression. They all ignore case in matching, if the pattern contains no upper-case letters and case-fold-search is non-nil. Aside from occur and its variants, all operate on the text from point to the end of the buffer, or on the region if it is active.  M-x multi-isearch-buffers Prompt for one or more buffer names, ending with ; then, begin a multi-buffer incremental search in those buffers. (If the search fails in one buffer, the next C-s tries searching the next specified buffer, and so forth.) With a prefix argument, prompt for a regexp and begin a multi-buffer incremental search in buffers matching that regexp. M-x multi-isearch-buffers-regexp This command is just like multi-isearch-buffers, except it performs an incremental regexp search. M-x occur Prompt for a regexp, and display a list showing each line in the buffer that contains a match for it. To limit the search to part of the buffer, narrow to that part (see Narrowing). A numeric argument n specifies that n lines of context are to be displayed before and after each matching line. In the *Occur* buffer, you can click on each entry, or move point there and type , to visit the corresponding position in the buffer that was searched. o and C-o display the match in another window; C-o does not select it. Alternatively, you can use the C-x  (next-error) command to visit the occurrences one by one (see Compilation Mode). Typing e in the *Occur* buffer switches to Occur Edit mode, in which edits made to the entries are also applied to the text in the originating buffer. Type C-c C-c to return to Occur mode. The command M-x list-matching-lines is a synonym for M-x occur. M-s o Run occur using the search string of the last incremental string search. You can also run M-s o when an incremental search is active; this uses the current search string. M-x multi-occur This command is just like occur, except it can search through multiple buffers. It asks you to specify the buffer names one by one. M-x multi-occur-in-matching-buffers This command is similar to multi-occur, except the buffers to search are specified by a regular expression that matches visited file names. With a prefix argument, it uses the regular expression to match buffer names instead. M-x how-many Prompt for a regexp, and print the number of matches for it in the buffer after point. If the region is active, this operates on the region instead. M-x flush-lines Prompt for a regexp, and delete each line that contains a match for it, operating on the text after point. This command deletes the current line if it contains a match starting after point. If the region is active, it operates on the region instead; if a line partially contained in the region contains a match entirely contained in the region, it is deleted. If a match is split across lines, flush-lines deletes all those lines. It deletes the lines before starting to look for the next match; hence, it ignores a match starting on the same line at which another match ended. M-x keep-lines Prompt for a regexp, and delete each line that does not contain a match for it, operating on the text after point. If point is not at the beginning of a line, this command always keeps the current line. If the region is active, the command operates on the region instead; it never deletes lines that are only partially contained in the region (a newline that ends a line counts as part of that line). If a match is split across lines, this command keeps all those lines. ## Commands For Fixing Typos In this chapter we describe commands that are useful when you catch a mistake while editing. The most fundamental of these commands is the undo command C-/ (also bound to C-x u and C-_). This undoes a single command, or a part of a command (as in the case of query-replace), or several consecutive character insertions. Consecutive repetitions of C-/ undo earlier and earlier changes, back to the limit of the undo information available. Aside from the commands described here, you can erase text using deletion commands such as <DEL> (delete-backward-char). These were described earlier in this manual. See Erasing. • Undo: The Undo commands. • Transpose: Exchanging two characters, words, lines, lists... • Fixing Case: Correcting case of last word entered. • Spelling: Apply spelling checker to a word, or a whole file. ## Undo The undo command reverses recent changes in the buffer's text. Each buffer records changes individually, and the undo command always applies to the current buffer. You can undo all the changes in a buffer for as far back as the buffer's records go. Usually, each editing command makes a separate entry in the undo records, but some commands such as query-replace divide their changes into multiple entries for flexibility in undoing. Consecutive character insertion commands are usually grouped together into a single undo record, to make undoing less tedious.  C-/, C-x u, C-_ Undo one entry in the current buffer's undo records (undo). To begin to undo, type C-/ (or its aliases, C-_ or C-x u). This undoes the most recent change in the buffer, and moves point back to where it was before that change. Consecutive repetitions of C-/ (or its aliases) undo earlier and earlier changes in the current buffer. If all the recorded changes have already been undone, the undo command signals an error. Any command other than an undo command breaks the sequence of undo commands. Starting from that moment, the entire sequence of undo commands that you have just performed are themselves placed into the undo record, as a single set of changes. Therefore, to re-apply changes you have undone, type C-f or any other command that harmlessly breaks the sequence of undoing; then type C-/ to undo the undo command. Alternatively, if you want to resume undoing, without redoing previous undo commands, use M-x undo-only. This is like undo, but will not redo changes you have just undone. If you notice that a buffer has been modified accidentally, the easiest way to recover is to type C-/ repeatedly until the stars disappear from the front of the mode line (see Mode Line). Whenever an undo command makes the stars disappear from the mode line, it means that the buffer contents are the same as they were when the file was last read in or saved. If you do not remember whether you changed the buffer deliberately, type C-/ once. When you see the last change you made undone, you will see whether it was an intentional change. If it was an accident, leave it undone. If it was deliberate, redo the change as described above. When there is an active region, any use of undo performs selective undo: it undoes the most recent change within the region, instead of the entire buffer. However, when Transient Mark mode is off (see Disabled Transient Mark), C-/ always operates on the entire buffer, ignoring the region. In this case, you can perform selective undo by supplying a prefix argument to the undo command: C-u C-/. To undo further changes in the same region, repeat the undo command (no prefix argument is needed). Some specialized buffers do not make undo records. Buffers whose names start with spaces never do; these buffers are used internally by Emacs to hold text that users don't normally look at or edit. When the undo information for a buffer becomes too large, Emacs discards the oldest records from time to time (during garbage collection). You can specify how much undo information to keep by setting the variables undo-limit, undo-strong-limit, and undo-outer-limit. Their values are expressed in bytes. The variable undo-limit sets a soft limit: Emacs keeps undo data for enough commands to reach this size, and perhaps exceed it, but does not keep data for any earlier commands beyond that. Its default value is 80000. The variable undo-strong-limit sets a stricter limit: any previous command (though not the most recent one) that pushes the size past this amount is forgotten. The default value of undo-strong-limit is 120000. Regardless of the values of those variables, the most recent change is never discarded unless it gets bigger than undo-outer-limit (normally 12,000,000). At that point, Emacs discards the undo data and warns you about it. This is the only situation in which you cannot undo the last command. If this happens, you can increase the value of undo-outer-limit to make it even less likely to happen in the future. But if you didn't expect the command to create such large undo data, then it is probably a bug. ## Transposing Text  C-t Transpose two characters (transpose-chars). M-t Transpose two words (transpose-words). C-M-t Transpose two balanced expressions (transpose-sexps). C-x C-t Transpose two lines (transpose-lines). The common error of transposing two characters can be fixed, when they are adjacent, with the C-t command (transpose-chars). Normally, C-t transposes the two characters on either side of point. When given at the end of a line, rather than transposing the last character of the line with the newline, which would be useless, C-t transposes the last two characters on the line. So, if you catch your transposition error right away, you can fix it with just a C-t. If you don't catch it so fast, you must move the cursor back between the two transposed characters before you type C-t. If you transposed a space with the last character of the word before it, the word motion commands are a good way of getting there. Otherwise, a reverse search (C-r) is often the best way. See Search. M-t transposes the word before point with the word after point (transpose-words). It moves point forward over a word, dragging the word preceding or containing point forward as well. The punctuation characters between the words do not move. For example, 'FOO, BAR' transposes into 'BAR, FOO' rather than 'BAR FOO,'. C-M-t (transpose-sexps) is a similar command for transposing two expressions (see Expressions), and C-x C-t (transpose-lines) exchanges lines. They work like M-t except as regards what units of text they transpose. A numeric argument to a transpose command serves as a repeat count: it tells the transpose command to move the character (word, expression, line) before or containing point across other characters (words, expressions, lines). For example, C-u 3 C-t moves the character before point forward across three other characters. It would change 'f-!-oobar' into 'oobf-!-ar'. This is equivalent to repeating C-t three times. C-u - 4 M-t moves the word before point backward across four words. C-u - C-M-t would cancel the effect of plain C-M-t. A numeric argument of zero is assigned a special meaning (because otherwise a command with a repeat count of zero would do nothing): to transpose the character (word, expression, line) ending after point with the one ending after the mark. ## Case Conversion  M-- M-l Convert last word to lower case. Note Meta-- is Meta-minus. M-- M-u Convert last word to all upper case. M-- M-c Convert last word to lower case with capital initial. A very common error is to type words in the wrong case. Because of this, the word case-conversion commands M-l, M-u and M-c have a special feature when used with a negative argument: they do not move the cursor. As soon as you see you have mistyped the last word, you can case-convert it and go on typing. See Case. ## Checking and Correcting Spelling This section describes the commands to check the spelling of a single word or of a portion of a buffer. These commands only work if the spelling checker program Aspell, Ispell or Hunspell is installed. These programs are not part of Emacs, but one of them is usually installed in GNU/Linux and other free operating systems. See Aspell.  M-$ Check and correct spelling of the word at point (ispell-word). If the region is active, do it for all words in the region instead. M-x ispell Check and correct spelling of all words in the buffer. If the region is active, do it for all words in the region instead. M-x ispell-buffer Check and correct spelling in the buffer. M-x ispell-region Check and correct spelling in the region. M-x ispell-message Check and correct spelling in a draft mail message, excluding cited material. M-x ispell-change-dictionary dict Restart the Aspell/Ispell/Hunspell process, using dict as the dictionary. M-x ispell-kill-ispell Kill the Aspell/Ispell/Hunspell subprocess. M-, Complete the word before point based on the spelling dictionary (ispell-complete-word). M-x flyspell-mode Enable Flyspell mode, which highlights all misspelled words. M-x flyspell-prog-mode Enable Flyspell mode for comments and strings only.

To check the spelling of the word around or before point, and optionally correct it as well, type M-$(ispell-word). If a region is active, M-$ checks the spelling of all words within the region. See Mark. (When Transient Mark mode is off, M-$always acts on the word around or before point, ignoring the region; see Disabled Transient Mark.) Similarly, the command M-x ispell performs spell-checking in the region if one is active, or in the entire buffer otherwise. The commands M-x ispell-buffer and M-x ispell-region explicitly perform spell-checking on the entire buffer or the region respectively. To check spelling in an email message you are writing, use M-x ispell-message; that command checks the whole buffer, except for material that is indented or appears to be cited from other messages. See Sending Mail. When one of these commands encounters what appears to be an incorrect word, it asks you what to do. It usually displays a list of numbered "near-misses"—words that are close to the incorrect word. Then you must type a single-character response. Here are the valid responses:  digit Replace the word, just this time, with one of the displayed near-misses. Each near-miss is listed with a digit; type that digit to select it. Skip this word—continue to consider it incorrect, but don't change it here. r new Replace the word, just this time, with new. (The replacement string will be rescanned for more spelling errors.) R new Replace the word with new, and do a query-replace so you can replace it elsewhere in the buffer if you wish. (The replacements will be rescanned for more spelling errors.) a Accept the incorrect word—treat it as correct, but only in this editing session. A Accept the incorrect word—treat it as correct, but only in this editing session and for this buffer. i Insert this word in your private dictionary file so that Aspell or Ispell or Hunspell will consider it correct from now on, even in future sessions. m Like i, but you can also specify dictionary completion information. u Insert the lower-case version of this word in your private dictionary file. l word Look in the dictionary for words that match word. These words become the new list of "near-misses"; you can select one of them as the replacement by typing a digit. You can use '*' in word as a wildcard. C-g, X Quit interactive spell checking, leaving point at the word that was being checked. You can restart checking again afterward with C-u M-$. x Quit interactive spell checking and move point back to where it was when you started spell checking. q Quit interactive spell checking and kill the spell-checker subprocess. ? Show the list of options.

In Text mode and related modes, M-<TAB> (ispell-complete-word) performs in-buffer completion based on spelling correction. Insert the beginning of a word, and then type M-<TAB>; this shows a list of completions. (If your window manager intercepts M-<TAB>, type <ESC> <TAB> or C-M-i.) Each completion is listed with a digit or character; type that digit or character to choose it.

Once started, the Aspell or Ispell or Hunspell subprocess continues to run, waiting for something to do, so that subsequent spell checking commands complete more quickly. If you want to get rid of the process, use M-x ispell-kill-ispell. This is not usually necessary, since the process uses no processor time except when you do spelling correction.

Ispell, Aspell and Hunspell look up spelling in two dictionaries: the standard dictionary and your personal dictionary. The standard dictionary is specified by the variable ispell-local-dictionary or, if that is nil, by the variable ispell-dictionary. If both are nil, the spelling program's default dictionary is used. The command M-x ispell-change-dictionary sets the standard dictionary for the buffer and then restarts the subprocess, so that it will use a different standard dictionary. Your personal dictionary is specified by the variable ispell-personal-dictionary. If that is nil, the spelling program looks for a personal dictionary in a default location.

A separate dictionary is used for word completion. The variable ispell-complete-word-dict specifies the file name of this dictionary. The completion dictionary must be different because it cannot use root and affix information. For some languages, there is a spell checking dictionary but no word completion dictionary.

Flyspell mode is a minor mode that performs automatic spell checking as you type. When it finds a word that it does not recognize, it highlights that word. Type M-x flyspell-mode to toggle Flyspell mode in the current buffer. To enable Flyspell mode in all text mode buffers, add flyspell-mode to text-mode-hook. See Hooks.

When Flyspell mode highlights a word as misspelled, you can click on it with Mouse-2 to display a menu of possible corrections and actions. You can also correct the word by editing it manually in any way you like.

Flyspell Prog mode works just like ordinary Flyspell mode, except that it only checks words in comments and string constants. This feature is useful for editing programs. Type M-x flyspell-prog-mode to enable or disable this mode in the current buffer. To enable this mode in all programming mode buffers, add flyspell-prog-mode to prog-mode-hook (see Hooks).

## Keyboard Macros

In this chapter we describe how to record a sequence of editing commands so you can repeat it conveniently later.

A keyboard macro is a command defined by an Emacs user to stand for another sequence of keys. For example, if you discover that you are about to type C-n M-d C-d forty times, you can speed your work by defining a keyboard macro to do C-n M-d C-d, and then executing it 39 more times.

You define a keyboard macro by executing and recording the commands that are its definition. Put differently, as you define a keyboard macro, the definition is being executed for the first time. This way, you can see the effects of your commands, so that you don't have to figure them out in your head. When you close the definition, the keyboard macro is defined and also has been, in effect, executed once. You can then do the whole thing over again by invoking the macro.

Keyboard macros differ from ordinary Emacs commands in that they are written in the Emacs command language rather than in Lisp. This makes it easier for the novice to write them, and makes them more convenient as temporary hacks. However, the Emacs command language is not powerful enough as a programming language to be useful for writing anything intelligent or general. For such things, Lisp must be used.

## Basic Macro Use

 Start defining a keyboard macro (kmacro-start-macro-or-insert-counter). If a keyboard macro is being defined, end the definition; otherwise, execute the most recent keyboard macro (kmacro-end-or-call-macro). C-u Re-execute last keyboard macro, then append keys to its definition. C-u C-u Append keys to the last keyboard macro without re-executing it. C-x C-k r Run the last keyboard macro on each line that begins in the region (apply-macro-to-region-lines).

To start defining a keyboard macro, type <F3>. From then on, your keys continue to be executed, but also become part of the definition of the macro. 'Def' appears in the mode line to remind you of what is going on. When you are finished, type <F4> (kmacro-end-or-call-macro) to terminate the definition. For example,

<F3> M-f foo <F4>

defines a macro to move forward a word and then insert 'foo'. Note that <F3> and <F4> do not become part of the macro.

After defining the macro, you can call it with <F4>. For the above example, this has the same effect as typing M-f foo again. (Note the two roles of the <F4> command: it ends the macro if you are in the process of defining one, or calls the last macro otherwise.) You can also supply <F4> with a numeric prefix argument 'n', which means to invoke the macro 'n' times. An argument of zero repeats the macro indefinitely, until it gets an error or you type C-g (or, on MS-DOS, C-<BREAK>).

The above example demonstrates a handy trick that you can employ with keyboard macros: if you wish to repeat an operation at regularly spaced places in the text, include a motion command as part of the macro. In this case, repeating the macro inserts the string 'foo' after each successive word.

After terminating the definition of a keyboard macro, you can append more keystrokes to its definition by typing C-u <F3>. This is equivalent to plain <F3> followed by retyping the whole definition so far. As a consequence, it re-executes the macro as previously defined. If you change the variable kmacro-execute-before-append to nil, the existing macro will not be re-executed before appending to it (the default is t). You can also add to the end of the definition of the last keyboard macro without re-executing it by typing C-u C-u <F3>.

When a command reads an argument with the minibuffer, your minibuffer input becomes part of the macro along with the command. So when you replay the macro, the command gets the same argument as when you entered the macro. For example,

<F3> C-a C-k C-x b foo <RET> C-y C-x b <RET> <F4>

defines a macro that kills the current line, yanks it into the buffer 'foo', then returns to the original buffer.

Most keyboard commands work as usual in a keyboard macro definition, with some exceptions. Typing C-g (keyboard-quit) quits the keyboard macro definition. Typing C-M-c (exit-recursive-edit) can be unreliable: it works as you'd expect if exiting a recursive edit that started within the macro, but if it exits a recursive edit that started before you invoked the keyboard macro, it also necessarily exits the keyboard macro too. Mouse events are also unreliable, even though you can use them in a keyboard macro: when the macro replays the mouse event, it uses the original mouse position of that event, the position that the mouse had while you were defining the macro. The effect of this may be hard to predict.

The command C-x C-k r (apply-macro-to-region-lines) repeats the last defined keyboard macro on each line that begins in the region. It does this line by line, by moving point to the beginning of the line and then executing the macro.

In addition to the <F3> and <F4> commands described above, Emacs also supports an older set of key bindings for defining and executing keyboard macros. To begin a macro definition, type C-x ( (kmacro-start-macro); as with <F3>, a prefix argument appends this definition to the last keyboard macro. To end a macro definition, type C-x ) (kmacro-end-macro). To execute the most recent macro, type C-x e (kmacro-end-and-call-macro). If you enter C-x e while defining a macro, the macro is terminated and executed immediately. Immediately after typing C-x e, you can type <e> repeatedly to immediately repeat the macro one or more times. You can also give C-x e a repeat argument, just like <F4>.

C-x ) can be given a repeat count as an argument. This means to repeat the macro right after defining it. The macro definition itself counts as the first repetition, since it is executed as you define it, so C-u 4 C-x ) executes the macro immediately 3 additional times.

## The Keyboard Macro Ring

All defined keyboard macros are recorded in the keyboard macro ring. There is only one keyboard macro ring, shared by all buffers.

 C-x C-k C-k Execute the keyboard macro at the head of the ring (kmacro-end-or-call-macro-repeat). C-x C-k C-n Rotate the keyboard macro ring to the next macro (defined earlier) (kmacro-cycle-ring-next). C-x C-k C-p Rotate the keyboard macro ring to the previous macro (defined later) (kmacro-cycle-ring-previous).

All commands which operate on the keyboard macro ring use the same C-x C-k prefix. Most of these commands can be executed and repeated immediately after each other without repeating the C-x C-k prefix. For example,

C-x C-k C-p C-p C-k C-k C-k C-n C-n C-k C-p C-k C-d

will rotate the keyboard macro ring to the "second previous" macro, execute the resulting head macro three times, rotate back to the original head macro, execute that once, rotate to the "previous" macro, execute that, and finally delete it from the macro ring.

The command C-x C-k C-k (kmacro-end-or-call-macro-repeat) executes the keyboard macro at the head of the macro ring. You can repeat the macro immediately by typing another C-k, or you can rotate the macro ring immediately by typing C-n or C-p.

When a keyboard macro is being defined, C-x C-k C-k behaves like <F4> except that, immediately afterward, you can use most key bindings of this section without the C-x C-k prefix. For instance, another C-k will re-execute the macro.

The commands C-x C-k C-n (kmacro-cycle-ring-next) and C-x C-k C-p (kmacro-cycle-ring-previous) rotate the macro ring, bringing the next or previous keyboard macro to the head of the macro ring. The definition of the new head macro is displayed in the echo area. You can continue to rotate the macro ring immediately by repeating just C-n and C-p until the desired macro is at the head of the ring. To execute the new macro ring head immediately, just type C-k.

Note that Emacs treats the head of the macro ring as the "last defined keyboard macro". For instance, <F4> will execute that macro, and C-x C-k n will give it a name.

The maximum number of macros stored in the keyboard macro ring is determined by the customizable variable kmacro-ring-max.

## The Keyboard Macro Counter

Each keyboard macro has an associated counter, which is initialized to 0 when you start defining the macro. This counter allows you to insert a number into the buffer that depends on the number of times the macro has been called. The counter is incremented each time its value is inserted into the buffer.

 In a keyboard macro definition, insert the keyboard macro counter value in the buffer (kmacro-start-macro-or-insert-counter). C-x C-k C-i Insert the keyboard macro counter value in the buffer (kmacro-insert-counter). C-x C-k C-c Set the keyboard macro counter (kmacro-set-counter). C-x C-k C-a Add the prefix arg to the keyboard macro counter (kmacro-add-counter). C-x C-k C-f Specify the format for inserting the keyboard macro counter (kmacro-set-format).

When you are defining a keyboard macro, the command <F3> (kmacro-start-macro-or-insert-counter) inserts the current value of the keyboard macro's counter into the buffer, and increments the counter by 1. (If you are not defining a macro, <F3> begins a macro definition instead. See Basic Keyboard Macro.) You can use a numeric prefix argument to specify a different increment. If you just specify a C-u prefix, that is the same as an increment of zero: it inserts the current counter value without changing it.

As an example, let us show how the keyboard macro counter can be used to build a numbered list. Consider the following key sequence:

<F3> C-a <F3> . <SPC> <F4>

As part of this keyboard macro definition, the string '0. ' was inserted into the beginning of the current line. If you now move somewhere else in the buffer and type <F4> to invoke the macro, the string '1. ' is inserted at the beginning of that line. Subsequent invocations insert '2. ', '3. ', and so forth.

The command C-x C-k C-i (kmacro-insert-counter) does the same thing as <F3>, but it can be used outside a keyboard macro definition. When no keyboard macro is being defined or executed, it inserts and increments the counter of the macro at the head of the keyboard macro ring.

The command C-x C-k C-c (kmacro-set-counter) sets the current macro counter to the value of the numeric argument. If you use it inside the macro, it operates on each repetition of the macro. If you specify just C-u as the prefix, while executing the macro, that resets the counter to the value it had at the beginning of the current repetition of the macro (undoing any increments so far in this repetition).

The command C-x C-k C-a (kmacro-add-counter) adds the prefix argument to the current macro counter. With just C-u as argument, it resets the counter to the last value inserted by any keyboard macro. (Normally, when you use this, the last insertion will be in the same macro and it will be the same counter.)

The command C-x C-k C-f (kmacro-set-format) prompts for the format to use when inserting the macro counter. The default format is '%d', which means to insert the number in decimal without any padding. You can exit with empty minibuffer to reset the format to this default. You can specify any format string that the format function accepts and that makes sense with a single integer extra argument. Do not put the format string inside double quotes when you insert it in the minibuffer.

If you use this command while no keyboard macro is being defined or executed, the new format affects all subsequent macro definitions. Existing macros continue to use the format in effect when they were defined. If you set the format while defining a keyboard macro, this affects the macro being defined from that point on, but it does not affect subsequent macros. Execution of the macro will, at each step, use the format in effect at that step during its definition. Changes to the macro format during execution of a macro, like the corresponding changes during its definition, have no effect on subsequent macros.

The format set by C-x C-k C-f does not affect insertion of numbers stored in registers.

If you use a register as a counter, incrementing it on each repetition of the macro, that accomplishes the same thing as a keyboard macro counter. See Number Registers. For most purposes, it is simpler to use a keyboard macro counter.

## Executing Macros with Variations

In a keyboard macro, you can create an effect similar to that of query-replace, in that the macro asks you each time around whether to make a change.

 C-x q When this point is reached during macro execution, ask for confirmation (kbd-macro-query).

While defining the macro, type C-x q at the point where you want the query to occur. During macro definition, the C-x q does nothing, but when you run the macro later, C-x q asks you interactively whether to continue.

The valid responses when C-x q asks are:

 (or y) Continue executing the keyboard macro. (or n) Skip the remainder of this repetition of the macro, and start right away with the next repetition. (or q) Skip the remainder of this repetition and cancel further repetitions. C-r Enter a recursive editing level, in which you can perform editing that is not part of the macro. When you exit the recursive edit using C-M-c, you are asked again how to continue with the keyboard macro. If you type a at this time, the rest of the macro definition is executed. It is up to you to leave point and the text in a state such that the rest of the macro will do what you want.

C-u C-x q, which is C-x q with a numeric argument, performs a completely different function. It enters a recursive edit reading input from the keyboard, both when you type it during the definition of the macro, and when it is executed from the macro. During definition, the editing you do inside the recursive edit does not become part of the macro. During macro execution, the recursive edit gives you a chance to do some particularized editing on each repetition. See Recursive Edit.

## Naming and Saving Keyboard Macros

 C-x C-k n Give a command name (for the duration of the Emacs session) to the most recently defined keyboard macro (kmacro-name-last-macro). C-x C-k b Bind the most recently defined keyboard macro to a key sequence (for the duration of the session) (kmacro-bind-to-key). M-x insert-kbd-macro Insert in the buffer a keyboard macro's definition, as Lisp code.

If you wish to save a keyboard macro for later use, you can give it a name using C-x C-k n (kmacro-name-last-macro). This reads a name as an argument using the minibuffer and defines that name to execute the last keyboard macro, in its current form. (If you later add to the definition of this macro, that does not alter the name's definition as a macro.) The macro name is a Lisp symbol, and defining it in this way makes it a valid command name for calling with M-x or for binding a key to with global-set-key (see Keymaps). If you specify a name that has a prior definition other than a keyboard macro, an error message is shown and nothing is changed.

You can also bind the last keyboard macro (in its current form) to a key, using C-x C-k b (kmacro-bind-to-key) followed by the key sequence you want to bind. You can bind to any key sequence in the global keymap, but since most key sequences already have other bindings, you should select the key sequence carefully. If you try to bind to a key sequence with an existing binding (in any keymap), this command asks you for confirmation before replacing the existing binding.

To avoid problems caused by overriding existing bindings, the key sequences C-x C-k 0 through C-x C-k 9 and C-x C-k A through C-x C-k Z are reserved for your keyboard macro bindings. In fact, to bind to one of these key sequences, you only need to type the digit or letter rather than the whole key sequences. For example,

C-x C-k b 4

will bind the last keyboard macro to the key sequence C-x C-k 4.

Once a macro has a command name, you can save its definition in a file. Then it can be used in another editing session. First, visit the file you want to save the definition in. Then use this command:

M-x insert-kbd-macro <RET> macroname <RET>

This inserts some Lisp code that, when executed later, will define the same macro with the same definition it has now. (You need not understand Lisp code to do this, because insert-kbd-macro writes the Lisp code for you.) Then save the file. You can load the file later with load-file (see Lisp Libraries). If the file you save in is your init file ~/.emacs (see Init File) then the macro will be defined each time you run Emacs.

If you give insert-kbd-macro a numeric argument, it makes additional Lisp code to record the keys (if any) that you have bound to macroname, so that the macro will be reassigned the same keys when you load the file.

## Editing a Keyboard Macro

 C-x C-k C-e Edit the last defined keyboard macro (kmacro-edit-macro). C-x C-k e name Edit a previously defined keyboard macro name (edit-kbd-macro). C-x C-k l Edit the last 300 keystrokes as a keyboard macro (kmacro-edit-lossage).

You can edit the last keyboard macro by typing C-x C-k C-e or C-x C-k <RET> (kmacro-edit-macro). This formats the macro definition in a buffer and enters a specialized major mode for editing it. Type C-h m once in that buffer to display details of how to edit the macro. When you are finished editing, type C-c C-c.

You can edit a named keyboard macro or a macro bound to a key by typing C-x C-k e (edit-kbd-macro). Follow that with the keyboard input that you would use to invoke the macro: C-x e or M-x name or some other key sequence.

You can edit the last 300 keystrokes as a macro by typing C-x C-k l (kmacro-edit-lossage).

## Stepwise Editing a Keyboard Macro

You can interactively replay and edit the last keyboard macro, one command at a time, by typing C-x C-k <SPC> (kmacro-step-edit-macro). Unless you quit the macro using q or C-g, the edited macro replaces the last macro on the macro ring.

This macro editing feature shows the last macro in the minibuffer together with the first (or next) command to be executed, and prompts you for an action. You can enter ? to get a summary of your options. These actions are available:

• <SPC> and y execute the current command, and advance to the next command in the keyboard macro.
• n, d, and <DEL> skip and delete the current command.
• f skips the current command in this execution of the keyboard macro, but doesn't delete it from the macro.
• <TAB> executes the current command, as well as all similar commands immediately following the current command; for example, <TAB> may be used to insert a sequence of characters (corresponding to a sequence of self-insert-command commands).
• c continues execution (without further editing) until the end of the keyboard macro. If execution terminates normally, the edited macro replaces the original keyboard macro.
• C-k skips and deletes the rest of the keyboard macro, terminates step-editing, and replaces the original keyboard macro with the edited macro.
• q and C-g cancels the step-editing of the keyboard macro; discarding any changes made to the keyboard macro.
• i KEY... C-j reads and executes a series of key sequences (not including the final C-j), and inserts them before the current command in the keyboard macro, without advancing over the current command.
• I KEY... reads one key sequence, executes it, and inserts it before the current command in the keyboard macro, without advancing over the current command.
• r KEY... C-j reads and executes a series of key sequences (not including the final C-j), and replaces the current command in the keyboard macro with them, advancing over the inserted key sequences.
• R KEY... reads one key sequence, executes it, and replaces the current command in the keyboard macro with that key sequence, advancing over the inserted key sequence.
• a KEY... C-j executes the current command, then reads and executes a series of key sequences (not including the final C-j), and inserts them after the current command in the keyboard macro; it then advances over the current command and the inserted key sequences.
• A KEY... C-j executes the rest of the commands in the keyboard macro, then reads and executes a series of key sequences (not including the final C-j), and appends them at the end of the keyboard macro; it then terminates the step-editing and replaces the original keyboard macro with the edited macro.

## File Handling

The operating system stores data permanently in named files, so most of the text you edit with Emacs comes from a file and is ultimately stored in a file.

To edit a file, you must tell Emacs to read the file and prepare a buffer containing a copy of the file's text. This is called visiting the file. Editing commands apply directly to text in the buffer; that is, to the copy inside Emacs. Your changes appear in the file itself only when you save the buffer back into the file.

In addition to visiting and saving files, Emacs can delete, copy, rename, and append to files, keep multiple versions of them, and operate on file directories.

## File Names

Many Emacs commands that operate on a file require you to specify the file name, using the minibuffer (see Minibuffer File).

While in the minibuffer, you can use the usual completion and history commands (see Minibuffer). Note that file name completion ignores file names whose extensions appear in the variable completion-ignored-extensions (see Options). Note also that most commands use "permissive completion with confirmation" for reading file names: you are allowed to submit a nonexistent file name, but if you type <RET> immediately after completing up to a nonexistent file name, Emacs prints '[Confirm]' and you must type a second <RET> to confirm. See Completion Exit, for details.

Each buffer has a default directory, stored in the buffer-local variable default-directory. Whenever Emacs reads a file name using the minibuffer, it usually inserts the default directory into the minibuffer as the initial contents. You can inhibit this insertion by changing the variable insert-default-directory to nil (see Minibuffer File). Regardless, Emacs always assumes that any relative file name is relative to the default directory, e.g., entering a file name without a directory specifies a file in the default directory.

When you visit a file, Emacs sets default-directory in the visiting buffer to the directory of its file. When you create a new buffer that is not visiting a file, via a command like C-x b, its default directory is usually copied from the buffer that was current at the time (see Select Buffer). You can use the command M-x pwd to see the value of default-directory in the current buffer. The command M-x cd prompts for a directory name, and sets the buffer's default-directory to that directory (doing this does not change the buffer's file name, if any).

As an example, when you visit the file /u/rms/gnu/gnu.tasks, the default directory is set to /u/rms/gnu/. If you invoke a command that reads a file name, entering just 'foo' in the minibuffer, with a directory omitted, specifies the file /u/rms/gnu/foo; entering '../.login' specifies /u/rms/.login; and entering 'new/foo' specifies /u/rms/gnu/new/foo.

When typing a file name into the minibuffer, you can make use of a couple of shortcuts: a double slash is interpreted as "ignore everything before the second slash in the pair", and '~/' is interpreted as your home directory. See Minibuffer File.

The character '$' is used to substitute an environment variable into a file name. The name of the environment variable consists of all the alphanumeric characters after the '$'; alternatively, it can be enclosed in braces after the '$'. For example, if you have used the shell command export FOO=rms/hacks to set up an environment variable named FOO, then both /u/$FOO/test.c and /u/${FOO}/test.c are abbreviations for /u/rms/hacks/test.c. If the environment variable is not defined, no substitution occurs, so that the character '$' stands for itself. Note that environment variables affect Emacs only if they are applied before Emacs is started.

To access a file with '$' in its name, if the '$' causes expansion, type ''. This pair is converted to a single '$' at the same time that variable substitution is performed for a single '$'. Alternatively, quote the whole file name with '/:' (see Quoted File Names). File names which begin with a literal '~' should also be quoted with '/:'.

You can include non-ASCII characters in file names. See File Name Coding.

## Visiting Files

 C-x C-f Visit a file (find-file). C-x C-r Visit a file for viewing, without allowing changes to it (find-file-read-only). C-x C-v Visit a different file instead of the one visited last (find-alternate-file). C-x 4 f Visit a file, in another window (find-file-other-window). Don't alter what is displayed in the selected window. C-x 5 f Visit a file, in a new frame (find-file-other-frame). Don't alter what is displayed in the selected frame. M-x find-file-literally Visit a file with no conversion of the contents.

Visiting a file means reading its contents into an Emacs buffer so you can edit them. Emacs makes a new buffer for each file that you visit.

To visit a file, type C-x C-f (find-file) and use the minibuffer to enter the name of the desired file. While in the minibuffer, you can abort the command by typing C-g. See File Names, for details about entering file names into minibuffers.

If the specified file exists but the system does not allow you to read it, an error message is displayed in the echo area. Otherwise, you can tell that C-x C-f has completed successfully by the appearance of new text on the screen, and by the buffer name shown in the mode line (see Mode Line). Emacs normally constructs the buffer name from the file name, omitting the directory name. For example, a file named /usr/rms/emacs.tex is visited in a buffer named 'emacs.tex'. If there is already a buffer with that name, Emacs constructs a unique name; the normal method is to append '<2>', '<3>', and so on, but you can select other methods. See Uniquify.

To create a new file, just visit it using the same command, C-x C-f. Emacs displays '(New file)' in the echo area, but in other respects behaves as if you had visited an existing empty file.

After visiting a file, the changes you make with editing commands are made in the Emacs buffer. They do not take effect in the visited file, until you save the buffer (see Saving). If a buffer contains changes that have not been saved, we say the buffer is modified. This implies that some changes will be lost if the buffer is not saved. The mode line displays two stars near the left margin to indicate that the buffer is modified.

If you visit a file that is already in Emacs, C-x C-f switches to the existing buffer instead of making another copy. Before doing so, it checks whether the file has changed since you last visited or saved it. If the file has changed, Emacs offers to reread it.

If you try to visit a file larger than large-file-warning-threshold (the default is 10000000, which is about 10 megabytes), Emacs asks you for confirmation first. You can answer y to proceed with visiting the file. Note, however, that Emacs cannot visit files that are larger than the maximum Emacs buffer size, which is limited by the amount of memory Emacs can allocate and by the integers that Emacs can represent (see Buffers). If you try, Emacs displays an error message saying that the maximum buffer size has been exceeded.

If the file name you specify contains shell-style wildcard characters, Emacs visits all the files that match it. (On case-insensitive filesystems, Emacs matches the wildcards disregarding the letter case.) Wildcards include '?', '*', and '[...]' sequences. To enter the wild card '?' in a file name in the minibuffer, you need to type C-q ?. See Quoted File Names, for information on how to visit a file whose name actually contains wildcard characters. You can disable the wildcard feature by customizing find-file-wildcards.

If you visit the wrong file unintentionally by typing its name incorrectly, type C-x C-v (find-alternate-file) to visit the file you really wanted. C-x C-v is similar to C-x C-f, but it kills the current buffer (after first offering to save it if it is modified). When C-x C-v reads the file name to visit, it inserts the entire default file name in the buffer, with point just after the directory part; this is convenient if you made a slight error in typing the name.

If you "visit" a file that is actually a directory, Emacs invokes Dired, the Emacs directory browser. See Dired. You can disable this behavior by setting the variable find-file-run-dired to nil; in that case, it is an error to try to visit a directory.

Files that are actually collections of other files, or file archives, are visited in special modes which invoke a Dired-like environment to allow operations on archive members. See File Archives, for more about these features.

If you visit a file that the operating system won't let you modify, or that is marked read-only, Emacs makes the buffer read-only too, so that you won't go ahead and make changes that you'll have trouble saving afterward. You can make the buffer writable with C-x C-q (read-only-mode). See Misc Buffer.

If you want to visit a file as read-only to protect yourself from entering changes accidentally, visit it with the command C-x C-r (find-file-read-only) instead of C-x C-f.

C-x 4 f (find-file-other-window) is like C-x C-f except that the buffer containing the specified file is selected in another window. The window that was selected before C-x 4 f continues to show the same buffer it was already showing. If this command is used when only one window is being displayed, that window is split in two, with one window showing the same buffer as before, and the other one showing the newly requested file. See Windows.

C-x 5 f (find-file-other-frame) is similar, but opens a new frame, or selects any existing frame showing the specified file. See Frames.

On graphical displays, there are two additional methods for visiting files. Firstly, when Emacs is built with a suitable GUI toolkit, commands invoked with the mouse (by clicking on the menu bar or tool bar) use the toolkit's standard "File Selection" dialog instead of prompting for the file name in the minibuffer. On GNU/Linux platforms, Emacs does this when built with GTK, LessTif, and Motif toolkits; on MS Windows and Mac, the GUI version does that by default. For information on how to customize this, see Dialog Boxes.

Secondly, Emacs supports "drag and drop": dropping a file into an ordinary Emacs window visits the file using that window. As an exception, dropping a file into a window displaying a Dired buffer moves or copies the file into the displayed directory. For details, see Drag and Drop, and Misc Dired Features.

Each time you visit a file, Emacs automatically scans its contents to detect what character encoding and end-of-line convention it uses, and converts these to Emacs's internal encoding and end-of-line convention within the buffer. When you save the buffer, Emacs performs the inverse conversion, writing the file to disk with its original encoding and end-of-line convention. See Coding Systems.

If you wish to edit a file as a sequence of ASCII characters with no special encoding or conversion, use the M-x find-file-literally command. This visits a file, like C-x C-f, but does not do format conversion, character code conversion (see Coding Systems), or automatic uncompression (see Compressed Files), and does not add a final newline because of require-final-newline (see Customize Save). If you have already visited the same file in the usual (non-literal) manner, this command asks you whether to visit it literally instead.

Two special hook variables allow extensions to modify the operation of visiting files. Visiting a file that does not exist runs the functions in find-file-not-found-functions; this variable holds a list of functions, which are called one by one (with no arguments) until one of them returns non-nil. This is not a normal hook, and the name ends in '-functions' rather than '-hook' to indicate that fact.

Successful visiting of any file, whether existing or not, calls the functions in find-file-hook, with no arguments. This variable is a normal hook. In the case of a nonexistent file, the find-file-not-found-functions are run first. See Hooks.

There are several ways to specify automatically the major mode for editing the file (see Choosing Modes), and to specify local variables defined for that file (see File Variables).

## Saving Files

Saving a buffer in Emacs means writing its contents back into the file that was visited in the buffer.

• Save Commands: Commands for saving files.
• Backup: How Emacs saves the old version of your file.
• Customize Save: Customizing the saving of files.
• Interlocking: How Emacs protects against simultaneous editing of one file by two users.
• Time Stamps: Emacs can update time stamps on saved files.

## Commands For Saving Files

These are the commands that relate to saving and writing files.

 C-x C-s Save the current buffer to its file (save-buffer). C-x s Save any or all buffers to their files (save-some-buffers). M-~ Forget that the current buffer has been changed (not-modified). With prefix argument (C-u), mark the current buffer as changed. C-x C-w Save the current buffer with a specified file name (write-file). M-x set-visited-file-name Change the file name under which the current buffer will be saved.

When you wish to save the file and make your changes permanent, type C-x C-s (save-buffer). After saving is finished, C-x C-s displays a message like this:

Wrote /u/rms/gnu/gnu.tasks

If the current buffer is not modified (no changes have been made in it since the buffer was created or last saved), saving is not really done, because it would have no effect. Instead, C-x C-s displays a message like this in the echo area:

(No changes need to be saved)

With a prefix argument, C-u C-x C-s, Emacs also marks the buffer to be backed up when the next save is done. See Backup.

The command C-x s (save-some-buffers) offers to save any or all modified buffers. It asks you what to do with each buffer. The possible responses are analogous to those of query-replace:

 y Save this buffer and ask about the rest of the buffers. n Don't save this buffer, but ask about the rest of the buffers. ! Save this buffer and all the rest with no more questions. Terminate save-some-buffers without any more saving. . Save this buffer, then exit save-some-buffers without even asking about other buffers. C-r View the buffer that you are currently being asked about. When you exit View mode, you get back to save-some-buffers, which asks the question again. d Diff the buffer against its corresponding file, so you can see what changes you would be saving. This calls the command diff-buffer-with-file (see Comparing Files). C-h Display a help message about these options.

C-x C-c, the key sequence to exit Emacs, invokes save-some-buffers and therefore asks the same questions.

If you have changed a buffer but do not wish to save the changes, you should take some action to prevent it. Otherwise, each time you use C-x s or C-x C-c, you are liable to save this buffer by mistake. One thing you can do is type M-~ (not-modified), which clears out the indication that the buffer is modified. If you do this, none of the save commands will believe that the buffer needs to be saved. ('~' is often used as a mathematical symbol for not'; thus M-~ is not', metafied.) Alternatively, you can cancel all the changes made since the file was visited or saved, by reading the text from the file again. This is called reverting. See Reverting. (You could also undo all the changes by repeating the undo command C-x u until you have undone all the changes; but reverting is easier.)

M-x set-visited-file-name alters the name of the file that the current buffer is visiting. It reads the new file name using the minibuffer. Then it marks the buffer as visiting that file name, and changes the buffer name correspondingly. set-visited-file-name does not save the buffer in the newly visited file; it just alters the records inside Emacs in case you do save later. It also marks the buffer as "modified" so that C-x C-s in that buffer will save.

If you wish to mark the buffer as visiting a different file and save it right away, use C-x C-w (write-file). This is equivalent to set-visited-file-name followed by C-x C-s, except that C-x C-w asks for confirmation if the file exists. C-x C-s used on a buffer that is not visiting a file has the same effect as C-x C-w; that is, it reads a file name, marks the buffer as visiting that file, and saves it there. The default file name in a buffer that is not visiting a file is made by combining the buffer name with the buffer's default directory (see File Names).

If the new file name implies a major mode, then C-x C-w switches to that major mode, in most cases. The command set-visited-file-name also does this. See Choosing Modes.

If Emacs is about to save a file and sees that the date of the latest version on disk does not match what Emacs last read or wrote, Emacs notifies you of this fact, because it probably indicates a problem caused by simultaneous editing and requires your immediate attention.

## Backing Up Files

On most operating systems, rewriting a file automatically destroys all record of what the file used to contain. Thus, saving a file from Emacs throws away the old contents of the file—or it would, except that Emacs carefully copies the old contents to another file, called the backup file, before actually saving.

Emacs makes a backup for a file only the first time the file is saved from a buffer. No matter how many times you subsequently save the file, its backup remains unchanged. However, if you kill the buffer and then visit the file again, a new backup file will be made.

For most files, the variable make-backup-files determines whether to make backup files. On most operating systems, its default value is t, so that Emacs does write backup files.

For files managed by a version control system (see Version Control), the variable vc-make-backup-files determines whether to make backup files. By default, it is nil, since backup files are redundant when you store all the previous versions in a version control system. See Options.

At your option, Emacs can keep either a single backup for each file, or make a series of numbered backup files for each file that you edit. See Backup Names.

The default value of the backup-enable-predicate variable prevents backup files being written for files in the directories used for temporary files, specified by temporary-file-directory or small-temporary-file-directory.

You can explicitly tell Emacs to make another backup file from a buffer, even though that buffer has been saved before. If you save the buffer with C-u C-x C-s, the version thus saved will be made into a backup file if you save the buffer again. C-u C-u C-x C-s saves the buffer, but first makes the previous file contents into a new backup file. C-u C-u C-u C-x C-s does both things: it makes a backup from the previous contents, and arranges to make another from the newly saved contents if you save again.

• Names: How backup files are named.
• Deletion: Emacs deletes excess numbered backups.
• Copying: Backups can be made by copying or renaming.

## Single or Numbered Backups

When Emacs makes a backup file, its name is normally constructed by appending '~' to the file name being edited; thus, the backup file for eval.c would be eval.c~.

If access control stops Emacs from writing backup files under the usual names, it writes the backup file as ~/.emacs.d/%backup%~. Only one such file can exist, so only the most recently made such backup is available.

Emacs can also make numbered backup files. Numbered backup file names contain '.~', the number, and another '~' after the original file name. Thus, the backup files of eval.c would be called eval.c.~1~, eval.c.~2~, and so on, all the way through names like eval.c.~259~ and beyond.

The variable version-control determines whether to make single backup files or multiple numbered backup files. Its possible values are:

 nil Make numbered backups for files that have numbered backups already. Otherwise, make single backups. This is the default. t Make numbered backups. never Never make numbered backups; always make single backups.

The usual way to set this variable is globally, through your init file or the customization buffer. However, you can set version-control locally in an individual buffer to control the making of backups for that buffer's file (see Locals). You can have Emacs set version-control locally whenever you visit a given file (see File Variables). Some modes, such as Rmail mode, set this variable.

If you set the environment variable VERSION_CONTROL, to tell various GNU utilities what to do with backup files, Emacs also obeys the environment variable by setting the Lisp variable version-control accordingly at startup. If the environment variable's value is 't' or 'numbered', then version-control becomes t; if the value is 'nil' or 'existing', then version-control becomes nil; if it is 'never' or 'simple', then version-control becomes never.

You can customize the variable backup-directory-alist to specify that files matching certain patterns should be backed up in specific directories. This variable applies to both single and numbered backups. A typical use is to add an element ("." . dir) to make all backups in the directory with absolute name dir; Emacs modifies the backup file names to avoid clashes between files with the same names originating in different directories. Alternatively, adding, ("." . ".~") would make backups in the invisible subdirectory .~ of the original file's directory. Emacs creates the directory, if necessary, to make the backup.

If you define the variable make-backup-file-name-function to a suitable Lisp function, that overrides the usual way Emacs constructs backup file names.

## Automatic Deletion of Backups

To prevent excessive consumption of disk space, Emacs can delete numbered backup versions automatically. Generally Emacs keeps the first few backups and the latest few backups, deleting any in between. This happens every time a new backup is made.

The two variables kept-old-versions and kept-new-versions control this deletion. Their values are, respectively, the number of oldest (lowest-numbered) backups to keep and the number of newest (highest-numbered) ones to keep, each time a new backup is made. The backups in the middle (excluding those oldest and newest) are the excess middle versions: those backups are deleted. These variables' values are used when it is time to delete excess versions, just after a new backup version is made; the newly made backup is included in the count in kept-new-versions. By default, both variables are 2.

If delete-old-versions is t, Emacs deletes the excess backup files silently. If it is nil, the default, Emacs asks you whether it should delete the excess backup versions. If it has any other value, then Emacs never automatically deletes backups.

Dired's . (Period) command can also be used to delete old versions. See Dired Deletion.

## Copying vs. Renaming

Backup files can be made by copying the old file or by renaming it. This makes a difference when the old file has multiple names (hard links). If the old file is renamed into the backup file, then the alternate names become names for the backup file. If the old file is copied instead, then the alternate names remain names for the file that you are editing, and the contents accessed by those names will be the new contents.

The method of making a backup file may also affect the file's owner and group. If copying is used, these do not change. If renaming is used, you become the file's owner, and the file's group becomes the default (different operating systems have different defaults for the group).

The choice of renaming or copying is made as follows:

• If the variable backup-by-copying is non-nil (the default is nil), use copying.
• Otherwise, if the variable backup-by-copying-when-linked is non-nil (the default is nil), and the file has multiple names, use copying.
• Otherwise, if the variable backup-by-copying-when-mismatch is non-nil (the default is t), and renaming would change the file's owner or group, use copying. If you change backup-by-copying-when-mismatch to nil, Emacs checks the numeric user-id of the file's owner. If this is higher than backup-by-copying-when-privileged-mismatch, then it behaves as though backup-by-copying-when-mismatch is non-nil anyway.
• Otherwise, renaming is the default choice.

When a file is managed with a version control system (see Version Control), Emacs does not normally make backups in the usual way for that file. But check-in and check-out are similar in some ways to making backups. One unfortunate similarity is that these operations typically break hard links, disconnecting the file name you visited from any alternate names for the same file. This has nothing to do with Emacs—the version control system does it.

## Customizing The Saving of Files

If the value of the variable require-final-newline is t, saving or writing a file silently puts a newline at the end if there isn't already one there. If the value is visit, Emacs adds a newline at the end of any file that doesn't have one, just after it visits the file. (This marks the buffer as modified, and you can undo it.) If the value is visit-save, Emacs adds such newlines both on visiting and on saving. If the value is nil, Emacs leaves the end of the file unchanged; any other non-nil value means to asks you whether to add a newline. The default is nil.

Some major modes are designed for specific kinds of files that are always supposed to end in newlines. Such major modes set the variable require-final-newline to the value of mode-require-final-newline, which defaults to t. By setting the latter variable, you can control how these modes handle final newlines.

When Emacs saves a file, it invokes the fsync system call to force the data immediately out to disk. This is important for safety if the system crashes or in case of power outage. However, it can be disruptive on laptops using power saving, as it may force a disk spin-up each time you save a file. If you accept an increased risk of data loss, you can set write-region-inhibit-fsync to a non-nil value to disable the synchronization.

## Protection against Simultaneous Editing

Simultaneous editing occurs when two users visit the same file, both make changes, and then both save them. If nobody is informed that this is happening, whichever user saves first would later find that his changes were lost.

On some systems, Emacs notices immediately when the second user starts to change the file, and issues an immediate warning. On all systems, Emacs checks when you save the file, and warns if you are about to overwrite another user's changes. You can prevent loss of the other user's work by taking the proper corrective action instead of saving the file.

When you make the first modification in an Emacs buffer that is visiting a file, Emacs records that the file is locked by you. (It does this by creating a specially-named symbolic link in the same directory.) Emacs removes the lock when you save the changes. The idea is that the file is locked whenever an Emacs buffer visiting it has unsaved changes.

You can prevent the creation of lock files by setting the variable create-lockfiles to nil. Caution: by doing so you will lose the benefits that this feature provides.

If you begin to modify the buffer while the visited file is locked by someone else, this constitutes a collision. When Emacs detects a collision, it asks you what to do, by calling the Lisp function ask-user-about-lock. You can redefine this function for the sake of customization. The standard definition of this function asks you a question and accepts three possible answers:

 s Steal the lock. Whoever was already changing the file loses the lock, and you gain the lock. p Proceed. Go ahead and edit the file despite its being locked by someone else. q Quit. This causes an error (file-locked), and the buffer contents remain unchanged—the modification you were trying to make does not actually take place.

If Emacs or the operating system crashes, this may leave behind lock files that are stale, so you may occasionally get warnings about spurious collisions. When you determine that the collision is spurious, just use p to tell Emacs to go ahead anyway.

Note that locking works on the basis of a file name; if a file has multiple names, Emacs does not prevent two users from editing it simultaneously under different names.

A lock file cannot be written in some circumstances, e.g., if Emacs lacks the system permissions or the system does not support symbolic links. In these cases, Emacs can still detect the collision when you try to save a file, by checking the file's last-modification date. If the file has changed since the last time Emacs visited or saved it, that implies that changes have been made in some other way, and will be lost if Emacs proceeds with saving. Emacs then displays a warning message and asks for confirmation before saving; answer yes to save, and no or C-g cancel the save.

If you are notified that simultaneous editing has already taken place, one way to compare the buffer to its file is the M-x diff-buffer-with-file command. See Comparing Files.

 M-x shadow-initialize Set up file shadowing. M-x shadow-define-literal-group Declare a single file to be shared between sites. M-x shadow-define-regexp-group Make all files that match each of a group of files be shared between hosts. M-x shadow-define-cluster name Define a shadow file cluster name. M-x shadow-copy-files Copy all pending shadow files. M-x shadow-cancel Cancel the instruction to shadow some files.

You can arrange to keep identical shadow copies of certain files in more than one place—possibly on different machines. To do this, first you must set up a shadow file group, which is a set of identically-named files shared between a list of sites. The file group is permanent and applies to further Emacs sessions as well as the current one. Once the group is set up, every time you exit Emacs, it will copy the file you edited to the other files in its group. You can also do the copying without exiting Emacs, by typing M-x shadow-copy-files.

To set up a shadow file group, use M-x shadow-define-literal-group or M-x shadow-define-regexp-group. See their documentation strings for further information.

Before copying a file to its shadows, Emacs asks for confirmation. You can answer "no" to bypass copying of this file, this time. If you want to cancel the shadowing permanently for a certain file, use M-x shadow-cancel to eliminate or change the shadow file group.

A shadow cluster is a group of hosts that share directories, so that copying to or from one of them is sufficient to update the file on all of them. Each shadow cluster has a name, and specifies the network address of a primary host (the one we copy files to), and a regular expression that matches the hostnames of all the other hosts in the cluster. You can define a shadow cluster with M-x shadow-define-cluster.

## Updating Time Stamps Automatically

You can arrange to put a time stamp in a file, so that it is updated automatically each time you edit and save the file. The time stamp must be in the first eight lines of the file, and you should insert it like this:

Time-stamp: <>

or like this:

Time-stamp: " "

Then add the function time-stamp to the hook before-save-hook (see Hooks). When you save the file, this function then automatically updates the time stamp with the current date and time. You can also use the command M-x time-stamp to update the time stamp manually. For other customizations, see the Custom group time-stamp. Note that the time stamp is formatted according to your locale setting (see Environment).

## Reverting the Buffer

If you have made extensive changes to a file-visiting buffer and then change your mind, you can revert the changes and go back to the saved version of the file. To do this, type M-x revert-buffer. Since reverting unintentionally could lose a lot of work, Emacs asks for confirmation first.

The revert-buffer command tries to position point in such a way that, if the file was edited only slightly, you will be at approximately the same part of the text as before. But if you have made major changes, point may end up in a totally different location.

Reverting marks the buffer as "not modified". It also clears the buffer's undo history (see Undo). Thus, the reversion cannot be undone: if you change your mind yet again, you can't use the undo commands to bring the reverted changes back.

Some kinds of buffers that are not associated with files, such as Dired buffers, can also be reverted. For them, reverting means recalculating their contents. Buffers created explicitly with C-x b cannot be reverted; revert-buffer reports an error if you try.

When you edit a file that changes automatically and frequently -- for example, a log of output from a process that continues to run -- it may be useful for Emacs to revert the file without querying you. To request this behavior, set the variable revert-without-query to a list of regular expressions. When a file name matches one of these regular expressions, find-file and revert-buffer will revert it automatically if it has changed, provided the buffer itself is not modified. (If you have edited the text, it would be wrong to discard your changes.)

You can also tell Emacs to revert buffers periodically. To do this for a specific buffer, enable the minor mode Auto-Revert mode by typing M-x auto-revert-mode. This automatically reverts the current buffer every five seconds; you can change the interval through the variable auto-revert-interval. To do the same for all file buffers, type M-x global-auto-revert-mode to enable Global Auto-Revert mode. These minor modes do not check or revert remote files, because that is usually too slow.

One use of Auto-Revert mode is to "tail" a file such as a system log, so that changes made to that file by other programs are continuously displayed. To do this, just move the point to the end of the buffer, and it will stay there as the file contents change. However, if you are sure that the file will only change by growing at the end, use Auto-Revert Tail mode instead (auto-revert-tail-mode). It is more efficient for this. Auto-Revert Tail mode works also for remote files.

See VC Undo, for commands to revert to earlier versions of files under version control. See VC Mode Line, for Auto Revert peculiarities when visiting files under version control.

## Auto-Reverting Non-File Buffers

Global Auto Revert Mode normally only reverts file buffers. There are two ways to auto-revert certain non-file buffers: by enabling Auto Revert Mode in those buffers (using M-x auto-revert-mode); and by setting global-auto-revert-non-file-buffers to a non-nil value. The latter enables Auto Reverting for all types of buffers for which it is implemented (listed in the menu below).

Like file buffers, non-file buffers should normally not revert while you are working on them, or while they contain information that might get lost after reverting. Therefore, they do not revert if they are "modified". This can get tricky, because deciding when a non-file buffer should be marked modified is usually more difficult than for file buffers.

Another tricky detail is that, for efficiency reasons, Auto Revert often does not try to detect all possible changes in the buffer, only changes that are "major" or easy to detect. Hence, enabling auto-reverting for a non-file buffer does not always guarantee that all information in the buffer is up-to-date, and does not necessarily make manual reverts useless.

At the other extreme, certain buffers automatically revert every auto-revert-interval seconds. (This currently only applies to the Buffer Menu.) In this case, Auto Revert does not print any messages while reverting, even when auto-revert-verbose is non-nil.

The details depend on the particular types of buffers and are explained in the corresponding sections.

If auto-reverting of non-file buffers is enabled, the Buffer Menu automatically reverts every auto-revert-interval seconds, whether there is a need for it or not. (It would probably take longer to check whether there is a need than to actually revert.)

If the Buffer Menu inappropriately gets marked modified, just revert it manually using g and auto-reverting will resume. However, if you marked certain buffers to get deleted or to be displayed, you have to be careful, because reverting erases all marks. The fact that adding marks sets the buffer's modified flag prevents Auto Revert from automatically erasing the marks.

## Auto-Reverting Dired Buffers

Auto-reverting Dired buffers currently works on GNU or Unix style operating systems. It may not work satisfactorily on some other systems.

Dired buffers only auto-revert when the file list of the buffer's main directory changes (e.g., when a new file is added). They do not auto-revert when information about a particular file changes (e.g., when the size changes) or when inserted subdirectories change. To be sure that all listed information is up to date, you have to manually revert using g, even if auto-reverting is enabled in the Dired buffer. Sometimes, you might get the impression that modifying or saving files listed in the main directory actually does cause auto-reverting. This is because making changes to a file, or saving it, very often causes changes in the directory itself; for instance, through backup files or auto-save files. However, this is not guaranteed.

If the Dired buffer is marked modified and there are no changes you want to protect, then most of the time you can make auto-reverting resume by manually reverting the buffer using g. There is one exception. If you flag or mark files, you can safely revert the buffer. This will not erase the flags or marks (unless the marked file has been deleted, of course). However, the buffer will stay modified, even after reverting, and auto-reverting will not resume. This is because, if you flag or mark files, you may be working on the buffer and you might not want the buffer to change without warning. If you want auto-reverting to resume in the presence of marks and flags, mark the buffer non-modified using M-~. However, adding, deleting or changing marks or flags will mark it modified again.

Remote Dired buffers are not auto-reverted (because it may be slow). Neither are Dired buffers for which you used shell wildcards or file arguments to list only some of the files. *Find* and *Locate* buffers do not auto-revert either.

This section is intended for Elisp programmers who would like to add support for auto-reverting new types of buffers.

To support auto-reverting the buffer must first of all have a revert-buffer-function. See Reverting.

Also, it must have a buffer-stale-function.

 buffer-stale-function The value of this variable is a function to check whether a non-file buffer needs reverting. This should be a function with one optional argument noconfirm. The function should return non-nil if the buffer should be reverted. The buffer is current when this function is called. While this function is mainly intended for use in auto-reverting, it could be used for other purposes as well. For instance, if auto-reverting is not enabled, it could be used to warn the user that the buffer needs reverting. The idea behind the noconfirm argument is that it should be t if the buffer is going to be reverted without asking the user and nil if the function is just going to be used to warn the user that the buffer is out of date. In particular, for use in auto-reverting, noconfirm is t. If the function is only going to be used for auto-reverting, you can ignore the noconfirm argument. If you just want to automatically auto-revert every auto-revert-interval seconds (like the Buffer Menu), use: (set (make-local-variable 'buffer-stale-function) #'(lambda (&optional noconfirm) 'fast) )  in the buffer's mode function. The special return value 'fast' tells the caller that the need for reverting was not checked, but that reverting the buffer is fast. It also tells Auto Revert not to print any revert messages, even if auto-revert-verbose is non-nil. This is important, as getting revert messages every auto-revert-interval seconds can be very annoying. The information provided by this return value could also be useful if the function is consulted for purposes other than auto-reverting.

Once the buffer has a revert-buffer-function and a buffer-stale-function, several problems usually remain.

The buffer will only auto-revert if it is marked unmodified. Hence, you will have to make sure that various functions mark the buffer modified if and only if either the buffer contains information that might be lost by reverting, or there is reason to believe that the user might be inconvenienced by auto-reverting, because he is actively working on the buffer. The user can always override this by manually adjusting the modified status of the buffer. To support this, calling the revert-buffer-function on a buffer that is marked unmodified should always keep the buffer marked unmodified.

It is important to assure that point does not continuously jump around as a consequence of auto-reverting. Of course, moving point might be inevitable if the buffer radically changes.

You should make sure that the revert-buffer-function does not print messages that unnecessarily duplicate Auto Revert's own messages, displayed if auto-revert-verbose is t, and effectively override a nil value for auto-revert-verbose. Hence, adapting a mode for auto-reverting often involves getting rid of such messages. This is especially important for buffers that automatically revert every auto-revert-interval seconds.

If the new auto-reverting is part of Emacs, you should mention it in the documentation string of global-auto-revert-non-file-buffers.

Similarly, you should add a section to this chapter. This section should at the very least make clear whether enabling auto-reverting for the buffer reliably assures that all information in the buffer is completely up to date (or will be after auto-revert-interval seconds).

## Auto-Saving: Protecting Against Disasters

From time to time, Emacs automatically saves each visited file in a separate file, without altering the file you actually use. This is called auto-saving. It prevents you from losing more than a limited amount of work if the system crashes.

When Emacs determines that it is time for auto-saving, it considers each buffer, and each is auto-saved if auto-saving is enabled for it and it has been changed since the last time it was auto-saved. The message 'Auto-saving...' is displayed in the echo area during auto-saving, if any files are actually auto-saved. Errors occurring during auto-saving are caught so that they do not interfere with the execution of commands you have been typing.

• Files: The file where auto-saved changes are actually made until you save the file.
• Control: Controlling when and how often to auto-save.
• Recover: Recovering text from auto-save files.

## Auto-Save Files

Auto-saving does not normally save in the files that you visited, because it can be very undesirable to save a change that you did not want to make permanent. Instead, auto-saving is done in a different file called the auto-save file, and the visited file is changed only when you request saving explicitly (such as with C-x C-s).

Normally, the auto-save file name is made by appending '#' to the front and rear of the visited file name. Thus, a buffer visiting file foo.c is auto-saved in a file #foo.c#. Most buffers that are not visiting files are auto-saved only if you request it explicitly; when they are auto-saved, the auto-save file name is made by appending '#' to the front and rear of buffer name, then adding digits and letters at the end for uniqueness. For example, the *mail* buffer in which you compose messages to be sent might be auto-saved in a file named #*mail*#704juu. Auto-save file names are made this way unless you reprogram parts of Emacs to do something different (the functions make-auto-save-file-name and auto-save-file-name-p). The file name to be used for auto-saving in a buffer is calculated when auto-saving is turned on in that buffer.

The variable auto-save-file-name-transforms allows a degree of control over the auto-save file name. It lets you specify a series of regular expressions and replacements to transform the auto save file name. The default value puts the auto-save files for remote files (see Remote Files) into the temporary file directory on the local machine.

When you delete a substantial part of the text in a large buffer, auto save turns off temporarily in that buffer. This is because if you deleted the text unintentionally, you might find the auto-save file more useful if it contains the deleted text. To reenable auto-saving after this happens, save the buffer with C-x C-s, or use C-u 1 M-x auto-save-mode.

If you want auto-saving to be done in the visited file rather than in a separate auto-save file, set the variable auto-save-visited-file-name to a non-nil value. In this mode, there is no real difference between auto-saving and explicit saving.

A buffer's auto-save file is deleted when you save the buffer in its visited file. (You can inhibit this by setting the variable delete-auto-save-files to nil.) Changing the visited file name with C-x C-w or set-visited-file-name renames any auto-save file to go with the new visited name.

## Controlling Auto-Saving

Each time you visit a file, auto-saving is turned on for that file's buffer if the variable auto-save-default is non-nil (but not in batch mode; see Options). The default for this variable is t, so auto-saving is the usual practice for file-visiting buffers. To toggle auto-saving in the current buffer, type M-x auto-save-mode. Auto Save mode acts as a buffer-local minor mode (see Minor Modes).

Emacs auto-saves periodically based on how many characters you have typed since the last auto-save. The variable auto-save-interval specifies how many characters there are between auto-saves. By default, it is 300. Emacs doesn't accept values that are too small: if you customize auto-save-interval to a value less than 20, Emacs will behave as if the value is 20.

Auto-saving also takes place when you stop typing for a while. By default, it does this after 30 seconds of idleness (at this time, Emacs may also perform garbage collection. To change this interval, customize the variable auto-save-timeout. The actual time period is longer if the current buffer is long; this is a heuristic which aims to keep out of your way when you are editing long buffers, in which auto-save takes an appreciable amount of time. Auto-saving during idle periods accomplishes two things: first, it makes sure all your work is saved if you go away from the terminal for a while; second, it may avoid some auto-saving while you are actually typing.

Emacs also does auto-saving whenever it gets a fatal error. This includes killing the Emacs job with a shell command such as 'kill %emacs', or disconnecting a network connection.

You can perform an auto-save explicitly with the command M-x do-auto-save.

## Recovering Data From Auto-Saves

You can use the contents of an auto-save file to recover from a loss of data with the command M-x recover-file <RET> file <RET>. This visits file and then (after your confirmation) restores the contents from its auto-save file #file#. You can then save with C-x C-s to put the recovered text into file itself. For example, to recover file foo.c from its auto-save file #foo.c#, do:

M-x recover-file <RET> foo.c <RET> yes <RET> C-x C-s

Before asking for confirmation, M-x recover-file displays a directory listing describing the specified file and the auto-save file, so you can compare their sizes and dates. If the auto-save file is older, M-x recover-file does not offer to read it.

If Emacs or the computer crashes, you can recover all the files you were editing from their auto save files with the command M-x recover-session. This first shows you a list of recorded interrupted sessions. Move point to the one you choose, and type C-c C-c. Then recover-session asks about each of the files that were being edited during that session, asking whether to recover that file. If you answer y, it calls recover-file, which works in its normal fashion. It shows the dates of the original file and its auto-save file, and asks once again whether to recover that file.

When recover-session is done, the files you've chosen to recover are present in Emacs buffers. You should then save them. Only this—saving them—updates the files themselves.

Emacs records information about interrupted sessions in files named .saves-pid-hostname in the directory ~/.emacs.d/auto-save-list/. This directory is determined by the variable auto-save-list-file-prefix. If you set auto-save-list-file-prefix to nil, sessions are not recorded for recovery.

## File Name Aliases

Symbolic links and hard links both make it possible for several file names to refer to the same file. Hard links are alternate names that refer directly to the file; all the names are equally valid, and no one of them is preferred. By contrast, a symbolic link is a kind of defined alias: when foo is a symbolic link to bar, you can use either name to refer to the file, but bar is the real name, while foo is just an alias. More complex cases occur when symbolic links point to directories.

Normally, if you visit a file which Emacs is already visiting under a different name, Emacs displays a message in the echo area and uses the existing buffer visiting that file. This can happen on systems that support hard or symbolic links, or if you use a long file name on a system that truncates long file names, or on a case-insensitive file system. You can suppress the message by setting the variable find-file-suppress-same-file-warnings to a non-nil value. You can disable this feature entirely by setting the variable find-file-existing-other-name to nil: then if you visit the same file under two different names, you get a separate buffer for each file name.

If the variable find-file-visit-truename is non-nil, then the file name recorded for a buffer is the file's truename (made by replacing all symbolic links with their target names), rather than the name you specify. Setting find-file-visit-truename also implies the effect of find-file-existing-other-name.

Sometimes, a directory is ordinarily accessed through a symbolic link, and you may want Emacs to preferentially show its "linked" name. To do this, customize directory-abbrev-alist. Each element in this list should have the form (from . to), which means to replace from with to whenever from appears in a directory name. The from string is a regular expression (see Regexps). It is matched against directory names anchored at the first character, and should start with '\' (to support directory names with embedded newlines, which would defeat '^'). The to string should be an ordinary absolute directory name pointing to the same directory. Do not use '~' to stand for a home directory in the to string; Emacs performs these substitutions separately. Here's an example, from a system on which /home/fsf is normally accessed through a symbolic link named /fsf:

(("\\/home/fsf" . "/fsf"))

## File Directories

The file system groups files into directories. A directory listing is a list of all the files in a directory. Emacs provides commands to create and delete directories, and to make directory listings in brief format (file names only) and verbose format (sizes, dates, and authors included). Emacs also includes a directory browser feature called Dired; see Dired.

 C-x C-d dir-or-pattern Display a brief directory listing (list-directory). C-u C-x C-d dir-or-pattern Display a verbose directory listing. M-x make-directory dirname Create a new directory named dirname. M-x delete-directory dirname Delete the directory named dirname. If it isn't empty, you will be asked whether you want to delete it recursively.

The command to display a directory listing is C-x C-d (list-directory). It reads using the minibuffer a file name that is either a directory to be listed or a wildcard-containing pattern for the files to be listed. For example,

C-x C-d /u2/emacs/etc <RET>

lists all the files in directory /u2/emacs/etc. Here is an example of specifying a file name pattern:

C-x C-d /u2/emacs/src/*.c <RET>

Normally, C-x C-d displays a brief directory listing containing just file names. A numeric argument (regardless of value) tells it to make a verbose listing including sizes, dates, and owners (like 'ls -l').

The text of a directory listing is mostly obtained by running ls in an inferior process. Two Emacs variables control the switches passed to ls: list-directory-brief-switches is a string giving the switches to use in brief listings ("-CF" by default), and list-directory-verbose-switches is a string giving the switches to use in a verbose listing ("-l" by default).

In verbose directory listings, Emacs adds information about the amount of free space on the disk that contains the directory. To do this, it runs the program specified by directory-free-space-program with arguments directory-free-space-args.

The command M-x delete-directory prompts for a directory name using the minibuffer, and deletes the directory if it is empty. If the directory is not empty, you will be asked whether you want to delete it recursively. On systems that have a "Trash" (or "Recycle Bin") feature, you can make this command move the specified directory to the Trash instead of deleting it outright, by changing the variable delete-by-moving-to-trash to t. See Misc File Ops, for more information about using the Trash.

## Comparing Files

The command M-x diff prompts for two file names, using the minibuffer, and displays the differences between the two files in a buffer named *diff*. This works by running the diff program, using options taken from the variable diff-switches. The value of diff-switches should be a string; the default is "-c" to specify a context diff. See Diff, for more information about the diff program.

The output of the diff command is shown using a major mode called Diff mode.

The command M-x diff-backup compares a specified file with its most recent backup. If you specify the name of a backup file, diff-backup compares it with the source file that it is a backup of. In all other respects, this behaves like M-x diff.

The command M-x diff-buffer-with-file compares a specified buffer with its corresponding file. This shows you what changes you would make to the file if you save the buffer.

The command M-x compare-windows compares the text in the current window with that in the next window. (For more information about windows in Emacs, see Windows.) Comparison starts at point in each window, after pushing each initial point value on the mark ring in its respective buffer. Then it moves point forward in each window, one character at a time, until it reaches characters that don't match. Then the command exits.

If point in the two windows is followed by non-matching text when the command starts, M-x compare-windows tries heuristically to advance up to matching text in the two windows, and then exits. So if you use M-x compare-windows repeatedly, each time it either skips one matching range or finds the start of another.

With a numeric argument, compare-windows ignores changes in whitespace. If the variable compare-ignore-case is non-nil, the comparison ignores differences in case as well. If the variable compare-ignore-whitespace is non-nil, compare-windows normally ignores changes in whitespace, and a prefix argument turns that off. You can use M-x smerge-mode to turn on Smerge mode, a minor mode for editing output from the diff3 program. This is typically the result of a failed merge from a version control system "update" outside VC, due to conflicting changes to a file. Smerge mode provides commands to resolve conflicts by selecting specific changes.

See Emerge, for the Emerge facility, which provides a powerful interface for merging files.

## Diff Mode

Diff mode is a major mode used for the output of M-x diff and other similar commands. This kind of output is called a patch, because it can be passed to the patch command to automatically apply the specified changes. To select Diff mode manually, type M-x diff-mode.

The changes specified in a patch are grouped into hunks, which are contiguous chunks of text that contain one or more changed lines. Hunks can also include unchanged lines to provide context for the changes. Each hunk is preceded by a hunk header, which specifies the old and new line numbers at which the hunk occurs. Diff mode highlights each hunk header, to distinguish it from the actual contents of the hunk.

You can edit a Diff mode buffer like any other buffer. (If it is read-only, you need to make it writable first. See Misc Buffer.) Whenever you change a hunk, Diff mode attempts to automatically correct the line numbers in the hunk headers, to ensure that the patch remains "correct". To disable automatic line number correction, change the variable diff-update-on-the-fly to nil.

Diff mode treats each hunk as an "error message", similar to Compilation mode. Thus, you can use commands such as C-x ' to visit the corresponding source locations. See Compilation Mode.

Also, Diff mode provides the following commands to navigate, manipulate and apply parts of patches:

 M-n Move to the next hunk-start (diff-hunk-next). This command has a side effect: it refines the hunk you move to, highlighting its changes with better granularity. To disable this feature, type M-x diff-auto-refine-mode to toggle off the minor mode Diff Auto-Refine mode. To disable Diff Auto Refine mode by default, add this to your init file (see Hooks): (add-hook 'diff-mode-hook (lambda () (diff-auto-refine-mode -1)))  M-p Move to the previous hunk-start (diff-hunk-prev). Like M-n, this has the side-effect of refining the hunk you move to, unless you disable Diff Auto-Refine mode. M-} Move to the next file-start, in a multi-file patch (diff-file-next). M-{ Move to the previous file-start, in a multi-file patch (diff-file-prev). M-k Kill the hunk at point (diff-hunk-kill). M-K In a multi-file patch, kill the current file part. (diff-file-kill). C-c C-a Apply this hunk to its target file (diff-apply-hunk). With a prefix argument of C-u, revert this hunk. C-c C-b Highlight the changes of the hunk at point with a finer granularity (diff-refine-hunk). This allows you to see exactly which parts of each changed line were actually changed. C-c C-c Go to the source file and line corresponding to this hunk (diff-goto-source). C-c C-e Start an Ediff session with the patch (diff-ediff-patch). C-c C-n Restrict the view to the current hunk (diff-restrict-view). See Narrowing. With a prefix argument of C-u, restrict the view to the current file of a multiple-file patch. To widen again, use C-x n w (widen). C-c C-r Reverse the direction of comparison for the entire buffer (diff-reverse-direction). C-c C-s Split the hunk at point (diff-split-hunk). This is for manually editing patches, and only works with the unified diff format produced by the -u or --unified options to the diff program. If you need to split a hunk in the context diff format produced by the -c or --context options to diff, first convert the buffer to the unified diff format with C-c C-u. C-c C-d Convert the entire buffer to the context diff format (diff-unified-context). With a prefix argument, convert only the text within the region. C-c C-u Convert the entire buffer to unified diff format (diff-context-unified). With a prefix argument, convert unified format to context format. When the mark is active, convert only the text within the region. C-c C-w Refine the current hunk so that it disregards changes in whitespace (diff-refine-hunk). C-x 4 A Generate a ChangeLog entry, like C-x 4 a does (see Change Log), for each one of the hunks (diff-add-change-log-entries-other-window). This creates a skeleton of the log of changes that you can later fill with the actual descriptions of the changes. C-x 4 a itself in Diff mode operates on behalf of the current hunk's file, but gets the function name from the patch itself. This is useful for making log entries for functions that are deleted by the patch.

Patches sometimes include trailing whitespace on modified lines, as an unintentional and undesired change. There are two ways to deal with this problem. Firstly, if you enable Whitespace mode in a Diff buffer (see Useless Whitespace), it automatically highlights trailing whitespace in modified lines. Secondly, you can use the command M-x diff-delete-trailing-whitespace, which searches for trailing whitespace in the lines modified by the patch, and removes that whitespace in both the patch and the patched source file(s). This command does not save the modifications that it makes, so you can decide whether to save the changes (the list of modified files is displayed in the echo area). With a prefix argument, it tries to modify the original source files rather than the patched source files.

## Miscellaneous File Operations

Emacs has commands for performing other operations on files. All operate on one file; they do not accept wildcard file names.

M-x delete-file prompts for a file and deletes it. If you are deleting many files in one directory, it may be more convenient to use Dired rather than delete-file. See Dired Deletion.

M-x move-file-to-trash moves a file into the system Trash (or Recycle Bin). This is a facility available on most operating systems; files that are moved into the Trash can be brought back later if you change your mind.

By default, Emacs deletion commands do not use the Trash. To use the Trash (when it is available) for common deletion commands, change the variable delete-by-moving-to-trash to t. This affects the commands M-x delete-file and M-x delete-directory (see Directories), as well as the deletion commands in Dired (see Dired Deletion). Supplying a prefix argument to M-x delete-file or M-x delete-directory makes them delete outright, instead of using the Trash, regardless of delete-by-moving-to-trash.

If a file is under version control (see Version Control), you should delete it using M-x vc-delete-file instead of M-x delete-file. See Delete/Rename.

M-x copy-file reads the file old and writes a new file named new with the same contents.

M-x copy-directory copies directories, similar to the cp -r shell command. It prompts for a directory old and a destination new. If new is an existing directory, it creates a copy of the old directory and puts it in new. If new is not an existing directory, it copies all the contents of old into a new directory named new.

M-x rename-file reads two file names old and new using the minibuffer, then renames file old as new. If the file name new already exists, you must confirm with yes or renaming is not done; this is because renaming causes the old meaning of the name new to be lost. If old and new are on different file systems, the file old is copied and deleted. If the argument new is just a directory name, the real new name is in that directory, with the same non-directory component as old. For example, M-x rename-file <RET> ~/foo <RET> /tmp <RET> renames ~/foo to /tmp/foo. The same rule applies to all the remaining commands in this section. All of them ask for confirmation when the new file name already exists, too.

If a file is under version control (see Version Control), you should rename it using M-x vc-rename-file instead of M-x rename-file. See VC Delete/Rename.

M-x add-name-to-file adds an additional name to an existing file without removing its old name. The new name is created as a "hard link" to the existing file. The new name must belong on the same file system that the file is on. On MS Windows, this command works only if the file resides in an NTFS file system. On MS-DOS, it works by copying the file.

M-x make-symbolic-link reads two file names target and linkname, then creates a symbolic link named linkname, which points at target. The effect is that future attempts to open file linkname will refer to whatever file is named target at the time the opening is done, or will get an error if the name target is nonexistent at that time. This command does not expand the argument target, so that it allows you to specify a relative name as the target of the link. On MS Windows, this command works only on MS Windows Vista and later.

M-x insert-file (also C-x i) inserts a copy of the contents of the specified file into the current buffer at point, leaving point unchanged before the contents. The position after the inserted contents is added to the mark ring, without activating the mark (see Mark Ring).

M-x insert-file-literally is like M-x insert-file, except the file is inserted "literally": it is treated as a sequence of ASCII characters with no special encoding or conversion, similar to the M-x find-file-literally command (see Visiting).

M-x write-region is the inverse of M-x insert-file; it copies the contents of the region into the specified file. M-x append-to-file adds the text of the region to the end of the specified file. See Accumulating Text. The variable write-region-inhibit-fsync applies to these commands, as well as saving files; see Customize Save.

M-x set-file-modes reads a file name followed by a file mode, and applies that file mode to the specified file. File modes, also called file permissions, determine whether a file can be read, written to, or executed, and by whom. This command reads file modes using the same symbolic or octal format accepted by the chmod command; for instance, 'u+x' means to add execution permission for the user who owns the file. It has no effect on operating systems that do not support file modes. chmod is a convenience alias for this function.

## Accessing Compressed Files

Emacs automatically uncompresses compressed files when you visit them, and automatically recompresses them if you alter them and save them. Emacs recognizes compressed files by their file names. File names ending in '.gz' indicate a file compressed with gzip. Other endings indicate other compression programs.

Automatic uncompression and compression apply to all the operations in which Emacs uses the contents of a file. This includes visiting it, saving it, inserting its contents into a buffer, loading it, and byte compiling it.

To disable this feature, type the command M-x auto-compression-mode. You can disable it permanently by customizing the variable auto-compression-mode.

## File Archives

A file whose name ends in '.tar' is normally an archive made by the tar program. Emacs views these files in a special mode called Tar mode which provides a Dired-like list of the contents (see Dired). You can move around through the list just as you would in Dired, and visit the subfiles contained in the archive. However, not all Dired commands are available in Tar mode.

If Auto Compression mode is enabled (see Compressed Files), then Tar mode is used also for compressed archives—files with extensions '.tgz', .tar.Z and .tar.gz.

The keys e, f and <RET> all extract a component file into its own buffer. You can edit it there, and if you save the buffer, the edited version will replace the version in the Tar buffer. Clicking with the mouse on the file name in the Tar buffer does likewise. v extracts a file into a buffer in View mode (see View Mode). o extracts the file and displays it in another window, so you could edit the file and operate on the archive simultaneously.

d marks a file for deletion when you later use x, and u unmarks a file, as in Dired. C copies a file from the archive to disk and R renames a file within the archive. g reverts the buffer from the archive on disk. The keys M, G, and O change the file's permission bits, group, and owner, respectively.

Saving the Tar buffer writes a new version of the archive to disk with the changes you made to the components.

You don't need the tar program to use Tar mode; Emacs reads the archives directly. However, accessing compressed archives requires the appropriate uncompression program.

A separate but similar Archive mode is used for arc, jar, lzh, zip, rar, 7z, and zoo archives, as well as exe files that are self-extracting executables.

The key bindings of Archive mode are similar to those in Tar mode, with the addition of the m key which marks a file for subsequent operations, and M-<DEL> which unmarks all the marked files. Also, the a key toggles the display of detailed file information, for those archive types where it won't fit in a single line. Operations such as renaming a subfile, or changing its mode or owner, are supported only for some of the archive formats.

Unlike Tar mode, Archive mode runs the archiving programs to unpack and repack archives. However, you don't need these programs to look at the archive table of contents, only to extract or manipulate the subfiles in the archive. Details of the program names and their options can be set in the 'Archive' Customize group.

## Remote Files

You can refer to files on other machines using a special file name syntax:

/host:filename
/[email protected]:filename
/[email protected]#port:filename
/method:[email protected]:filename
/method:[email protected]#port:filename

To carry out this request, Emacs uses a remote-login program such as ftp, ssh, rlogin, or telnet. You can always specify in the file name which method to use: for example, /ftp:[email protected]:filename uses FTP, whereas /ssh:[email protected]:filename uses ssh. When you don't specify a method in the file name, Emacs chooses the method as follows:

• If the hostname starts with 'ftp.' (with dot), Emacs uses FTP.
• If the username is 'ftp' or 'anonymous', Emacs uses FTP.
• If the variable tramp-default-method is set to 'ftp', Emacs uses FTP.
• If ssh-agent is running, Emacs uses scp.
• Otherwise, Emacs uses ssh.

You can entirely turn off the remote file name feature by setting the variable tramp-mode to nil. You can turn off the feature in individual cases by quoting the file name with '/:' (see Quoted File Names).

Remote file access through FTP is handled by the Ange-FTP package, which is documented in the following. Remote file access through the other methods is handled by the Tramp package, which has its own manual.

When the Ange-FTP package is used, Emacs logs in through FTP using the name user, if that is specified in the remote file name. If user is unspecified, Emacs logs in using your username on the local system; but if you set the variable ange-ftp-default-user to a string, that string is used instead. When logging in, Emacs may also ask for a password.

For performance reasons, Emacs does not make backup files for files accessed vian FTP by default. To make it do so, change the variable ange-ftp-make-backup-files to a non-nil value.

By default, auto-save files for remote files are made in the temporary file directory on the local machine, as specified by the variable auto-save-file-name-transforms. See Auto Save Files.

To visit files accessible by anonymous FTP, you use special usernames 'anonymous' or 'ftp'. Passwords for these usernames are handled specially. The variable ange-ftp-generate-anonymous-password controls what happens: if the value of this variable is a string, then that string is used as the password; if non-nil (the default), then the value of user-mail-address is used; if nil, then Emacs prompts you for a password as usual (see Passwords).

Sometimes you may be unable to access files on a remote machine because a firewall in between blocks the connection for security reasons. If you can log in on a gateway machine from which the target files are accessible, and whose FTP server supports gatewaying features, you can still use remote file names; all you have to do is specify the name of the gateway machine by setting the variable ange-ftp-gateway-host, and set ange-ftp-smart-gateway to t. Otherwise, you may be able to make remote file names work, but the procedure is complex. You can read the instructions by typing M-x finder-commentary <RET> ange-ftp <RET>.

## Quoted File Names

You can quote an absolute file name to prevent special characters and syntax in it from having their special effects. The way to do this is to add '/:' at the beginning.

For example, you can quote a local file name which appears remote, to prevent it from being treated as a remote file name. Thus, if you have a directory named /foo: and a file named bar in it, you can refer to that file in Emacs as '/:/foo:/bar'.

'/:' can also prevent '~' from being treated as a special character for a user's home directory. For example, /:/tmp/~hack refers to a file whose name is ~hack in directory /tmp.

Quoting with '/:' is also a way to enter in the minibuffer a file name that contains '$'. In order for this to work, the '/:' must be at the beginning of the minibuffer contents. (You can also double each '$'; see File Names with .) You can also quote wildcard characters with '/:', for visiting. For example, /:/tmp/foo*bar visits the file /tmp/foo*bar. Another method of getting the same result is to enter /tmp/foo[*]bar, which is a wildcard specification that matches only /tmp/foo*bar. However, in many cases there is no need to quote the wildcard characters because even unquoted they give the right result. For example, if the only file name in /tmp that starts with 'foo' and ends with 'bar' is foo*bar, then specifying /tmp/foo*bar will visit only /tmp/foo*bar. ## File Name Cache You can use the file name cache to make it easy to locate a file by name, without having to remember exactly where it is located. When typing a file name in the minibuffer, C-<tab> (file-cache-minibuffer-complete) completes it using the file name cache. If you repeat C-<tab>, that cycles through the possible completions of what you had originally typed. (However, note that the C-<tab> character cannot be typed on most text terminals.) The file name cache does not fill up automatically. Instead, you load file names into the cache using these commands:  M-x file-cache-add-directory directory Add each file name in directory to the file name cache. M-x file-cache-add-directory-using-find directory Add each file name in directory and all of its nested subdirectories to the file name cache. M-x file-cache-add-directory-using-locate directory Add each file name in directory and all of its nested subdirectories to the file name cache, using locate to find them all. M-x file-cache-add-directory-list variable Add each file name in each directory listed in variable to the file name cache. variable should be a Lisp variable whose value is a list of directory names, like load-path. M-x file-cache-clear-cache Clear the cache; that is, remove all file names from it. The file name cache is not persistent: it is kept and maintained only for the duration of the Emacs session. You can view the contents of the cache with the file-cache-display command. ## Convenience Features for Finding Files In this section, we introduce some convenient facilities for finding recently-opened files, reading file names from a buffer, and viewing image files. If you enable Recentf mode, with M-x recentf-mode, the 'File' menu includes a submenu containing a list of recently opened files. M-x recentf-save-list saves the current recent-file-list to a file, and M-x recentf-edit-list edits it. The M-x ffap command generalizes find-file with more powerful heuristic defaults (see FFAP), often based on the text at point. Partial Completion mode offers other features extending find-file, which can be used with ffap. See Options. Visiting image files automatically selects Image mode. In this major mode, you can type C-c C-c (image-toggle-display) to toggle between displaying the file as an image in the Emacs buffer, and displaying its underlying text (or raw byte) representation. Displaying the file as an image works only if Emacs is compiled with support for displaying such images. If the displayed image is wider or taller than the frame, the usual point motion keys (C-f, C-p, and so forth) cause different parts of the image to be displayed. If the image can be animated, the command <RET> (image-toggle-animation) starts or stops the animation. Animation plays once, unless the option image-animate-loop is non-nil. Currently, Emacs only supports animation in GIF files. If Emacs was compiled with support for the ImageMagick library, it can use ImageMagick to render a wide variety of images. The variable imagemagick-enabled-types lists the image types that Emacs may render using ImageMagick; each element in the list should be an internal ImageMagick name for an image type, as a symbol or an equivalent string (e.g., BMP for .bmp images). To enable ImageMagick for all possible image types, change imagemagick-enabled-types to t. The variable imagemagick-types-inhibit lists the image types which should never be rendered using ImageMagick, regardless of the value of imagemagick-enabled-types (the default list includes types like C and HTML, which ImageMagick can render as an "image" but Emacs should not). To disable ImageMagick entirely, change imagemagick-types-inhibit to t. The Image-Dired package can also be used to view images as thumbnails. See Image-Dired. ## Filesets If you regularly edit a certain group of files, you can define them as a fileset. This lets you perform certain operations, such as visiting, query-replace, and shell commands on all the files at once. To make use of filesets, you must first add the expression (filesets-init) to your init file (see Init File). This adds a 'Filesets' menu to the menu bar. The simplest way to define a fileset is by adding files to it one at a time. To add a file to fileset name, visit the file and type M-x filesets-add-buffer <RET> name <RET>. If there is no fileset name, this creates a new one, which initially contains only the current file. The command M-x filesets-remove-buffer removes the current file from a fileset. You can also edit the list of filesets directly, with M-x filesets-edit (or by choosing 'Edit Filesets' from the 'Filesets' menu). The editing is performed in a Customize buffer (see Easy Customization). Normally, a fileset is a simple list of files, but you can also define a fileset as a regular expression matching file names. Some examples of these more complicated filesets are shown in the Customize buffer. Remember to select 'Save for future sessions' if you want to use the same filesets in future Emacs sessions. You can use the command M-x filesets-open to visit all the files in a fileset, and M-x filesets-close to close them. Use M-x filesets-run-cmd to run a shell command on all the files in a fileset. These commands are also available from the 'Filesets' menu, where each existing fileset is represented by a submenu. See Version Control, for a different concept of "filesets": groups of files bundled together for version control operations. Filesets of that type are unnamed, and do not persist across Emacs sessions. ## Using Multiple Buffers The text you are editing in Emacs resides in an object called a buffer. Each time you visit a file, a buffer is used to hold the file's text. Each time you invoke Dired, a buffer is used to hold the directory listing. If you send a message with C-x m, a buffer is used to hold the text of the message. When you ask for a command's documentation, that appears in a buffer named *Help*. Each buffer has a unique name, which can be of any length. When a buffer is displayed in a window, its name is shown in the mode line (see Mode Line). The distinction between upper and lower case matters in buffer names. Most buffers are made by visiting files, and their names are derived from the files' names; however, you can also create an empty buffer with any name you want. A newly started Emacs has several buffers, including one named *scratch*, which can be used for evaluating Lisp expressions and is not associated with any file (see Lisp Interaction). At any time, one and only one buffer is selected; we call it the current buffer. We sometimes say that a command operates on "the buffer"; this really means that it operates on the current buffer. When there is only one Emacs window, the buffer displayed in that window is current. When there are multiple windows, the buffer displayed in the selected window is current. See Windows. Aside from its textual contents, each buffer records several pieces of information, such as what file it is visiting (if any), whether it is modified, and what major mode and minor modes are in effect (see Modes). These are stored in buffer-local variables—variables that can have a different value in each buffer. See Locals. A buffer's size cannot be larger than some maximum, which is defined by the largest buffer position representable by Emacs integers. This is because Emacs tracks buffer positions using that data type. For typical 64-bit machines, this maximum buffer size is 2^61 - 2 bytes, or about 2 EiB. For typical 32-bit machines, the maximum is usually 2^29 - 2 bytes, or about 512 MiB. Buffer sizes are also limited by the amount of memory in the system. • Select Buffer: Creating a new buffer or reselecting an old one. • List Buffers: Getting a list of buffers that exist. • Misc Buffer: Renaming; changing read-onlyness; copying text. • Kill Buffer: Killing buffers you no longer need. • Several Buffers: How to go through the list of all buffers and operate variously on several of them. • Indirect Buffers: An indirect buffer shares the text of another buffer. • Buffer Convenience: Convenience and customization features for buffer handling. ## Creating and Selecting Buffers  C-x b buffer Select or create a buffer named buffer (switch-to-buffer). C-x 4 b buffer Similar, but select buffer in another window (switch-to-buffer-other-window). C-x 5 b buffer Similar, but select buffer in a separate frame (switch-to-buffer-other-frame). C-x Select the previous buffer in the buffer list (previous-buffer). C-x Select the next buffer in the buffer list (next-buffer). C-u M-g M-g, C-u M-g g Read a number n and move to line n in the most recently selected buffer other than the current buffer. The C-x b (switch-to-buffer) command reads a buffer name using the minibuffer. Then it makes that buffer current, and displays it in the currently-selected window. An empty input specifies the buffer that was current most recently among those not now displayed in any window. While entering the buffer name, you can use the usual completion and history commands (see Minibuffer). Note that C-x b, and related commands, use "permissive completion with confirmation" for minibuffer completion: if you type <RET> immediately after completing up to a nonexistent buffer name, Emacs prints '[Confirm]' and you must type a second <RET> to submit that buffer name. See Completion Exit, for details. If you specify a buffer that does not exist, C-x b creates a new, empty buffer that is not visiting any file, and selects it for editing. The default value of the variable major-mode determines the new buffer's major mode; the default value is Fundamental mode. See Major Modes. One reason to create a new buffer is to use it for making temporary notes. If you try to save it, Emacs asks for the file name to use, and the buffer's major mode is re-established taking that file name into account (see Choosing Modes). For conveniently switching between a few buffers, use the commands C-x <LEFT> and C-x <RIGHT>. C-x <LEFT> (previous-buffer) selects the previous buffer (following the order of most recent selection in the current frame), while C-x <RIGHT> (next-buffer) moves through buffers in the reverse direction. To select a buffer in a window other than the current one, type C-x 4 b (switch-to-buffer-other-window). This prompts for a buffer name using the minibuffer, displays that buffer in another window, and selects that window. Similarly, C-x 5 b (switch-to-buffer-other-frame) prompts for a buffer name, displays that buffer in another frame, and selects that frame. If the buffer is already being shown in a window on another frame, Emacs selects that window and frame instead of creating a new frame. See Displaying Buffers, for how the C-x 4 b and C-x 5 b commands get the window and/or frame to display in. Also, C-x C-f, and any other command for visiting a file, can also be used to switch to an existing file-visiting buffer. See Visiting. C-u M-g M-g, that is goto-line with a plain prefix argument, reads a number n using the minibuffer, selects the most recently selected buffer other than the current buffer in another window, and then moves point to the beginning of line number n in that buffer. This is mainly useful in a buffer that refers to line numbers in another buffer: if point is on or just after a number, goto-line uses that number as the default for n. Note that prefix arguments other than just C-u behave differently. C-u 4 M-g M-g goes to line 4 in the current buffer, without reading a number from the minibuffer. (Remember that M-g M-g without prefix argument reads a number n and then moves to line number n in the current buffer. See Moving Point.) Emacs uses buffer names that start with a space for internal purposes. It treats these buffers specially in minor ways—for example, by default they do not record undo information. It is best to avoid using such buffer names yourself. ## Listing Existing Buffers  C-x C-b List the existing buffers (list-buffers). To display a list of existing buffers, type C-x C-b. Each line in the list shows one buffer's name, major mode and visited file. The buffers are listed in the order that they were current; the buffers that were current most recently come first. '.' in the first field of a line indicates that the buffer is current. '%' indicates a read-only buffer. '*' indicates that the buffer is "modified". If several buffers are modified, it may be time to save some with C-x s (see Save Commands). Here is an example of a buffer list: CRM Buffer Size Mode File . * .emacs 3294 Emacs-Lisp ~/.emacs % *Help* 101 Help search.c 86055 C ~/cvs/emacs/src/search.c % src 20959 Dired by name ~/cvs/emacs/src/ * *mail* 42 Mail % HELLO 1607 Fundamental ~/cvs/emacs/etc/HELLO % NEWS 481184 Outline ~/cvs/emacs/etc/NEWS *scratch* 191 Lisp Interaction * *Messages* 1554 Fundamental  The buffer *Help* was made by a help request (see Help); it is not visiting any file. The buffer src was made by Dired on the directory ~/cvs/emacs/src/. You can list only buffers that are visiting files by giving the command a prefix argument, as in C-u C-x C-b. list-buffers omits buffers whose names begin with a space, unless they visit files: such buffers are used internally by Emacs. ## Miscellaneous Buffer Operations  C-x C-q Toggle read-only status of buffer (read-only-mode). M-x rename-buffer name Change the name of the current buffer. M-x rename-uniquely Rename the current buffer by adding '' to the end. M-x view-buffer buffer Scroll through buffer buffer. See View Mode. A buffer can be read-only, which means that commands to change its contents are not allowed. The mode line indicates read-only buffers with '%%' or '%*' near the left margin. Read-only buffers are usually made by subsystems such as Dired and Rmail that have special commands to operate on the text; also by visiting a file whose access control says you cannot write it. The command C-x C-q (read-only-mode) makes a read-only buffer writable, and makes a writable buffer read-only. This works by setting the variable buffer-read-only, which has a local value in each buffer and makes the buffer read-only if its value is non-nil. If you change the option view-read-only to a non-nil value, making the buffer read-only with C-x C-q also enables View mode in the buffer (see View Mode). M-x rename-buffer changes the name of the current buffer. You specify the new name as a minibuffer argument; there is no default. If you specify a name that is in use for some other buffer, an error happens and no renaming is done. M-x rename-uniquely renames the current buffer to a similar name with a numeric suffix added to make it both different and unique. This command does not need an argument. It is useful for creating multiple shell buffers: if you rename the *shell* buffer, then do M-x shell again, it makes a new shell buffer named *shell*; meanwhile, the old shell buffer continues to exist under its new name. This method is also good for mail buffers, compilation buffers, and most Emacs features that create special buffers with particular names. (With some of these features, such as M-x compile, M-x grep, you need to switch to some other buffer before using the command again, otherwise it will reuse the current buffer despite the name change.) The commands M-x append-to-buffer and M-x insert-buffer can also be used to copy text from one buffer to another. See Accumulating Text. ## Killing Buffers If you continue an Emacs session for a while, you may accumulate a large number of buffers. You may then find it convenient to kill the buffers you no longer need. On most operating systems, killing a buffer releases its space back to the operating system so that other programs can use it. Here are some commands for killing buffers:  C-x k bufname Kill buffer bufname (kill-buffer). M-x kill-some-buffers Offer to kill each buffer, one by one. M-x kill-matching-buffers Offer to kill all buffers matching a regular expression. C-x k (kill-buffer) kills one buffer, whose name you specify in the minibuffer. The default, used if you type just <RET> in the minibuffer, is to kill the current buffer. If you kill the current buffer, another buffer becomes current: one that was current in the recent past but is not displayed in any window now. If you ask to kill a file-visiting buffer that is modified, then you must confirm with yes before the buffer is killed. The command M-x kill-some-buffers asks about each buffer, one by one. An answer of y means to kill the buffer, just like kill-buffer. This command ignores buffers whose names begin with a space, which are used internally by Emacs. The command M-x kill-matching-buffers prompts for a regular expression and kills all buffers whose names match that expression. See Regexps. Like kill-some-buffers, it asks for confirmation before each kill. This command normally ignores buffers whose names begin with a space, which are used internally by Emacs. To kill internal buffers as well, call kill-matching-buffers with a prefix argument. The Buffer Menu feature is also convenient for killing various buffers. See Several Buffers. If you want to do something special every time a buffer is killed, you can add hook functions to the hook kill-buffer-hook (see Hooks). If you run one Emacs session for a period of days, as many people do, it can fill up with buffers that you used several days ago. The command M-x clean-buffer-list is a convenient way to purge them; it kills all the unmodified buffers that you have not used for a long time. An ordinary buffer is killed if it has not been displayed for three days; however, you can specify certain buffers that should never be killed automatically, and others that should be killed if they have been unused for a mere hour. You can also have this buffer purging done for you, once a day, by enabling Midnight mode. Midnight mode operates each day at midnight; at that time, it runs clean-buffer-list, or whichever functions you have placed in the normal hook midnight-hook (see Hooks). To enable Midnight mode, use the Customization buffer to set the variable midnight-mode to t. See Easy Customization. ## Operating On Several Buffers  M-x buffer-menu Begin editing a buffer listing all Emacs buffers. M-x buffer-menu-other-window. Similar, but do it in another window. The Buffer Menu opened by C-x C-b (see List Buffers) does not merely list buffers. It also allows you to perform various operations on buffers, through an interface similar to Dired (see Dired). You can save buffers, kill them (here called deleting them, for consistency with Dired), or display them. To use the Buffer Menu, type C-x C-b and switch to the window displaying the *Buffer List* buffer. You can also type M-x buffer-menu to open the Buffer Menu in the selected window. Alternatively, the command M-x buffer-menu-other-window opens the Buffer Menu in another window, and selects that window. The Buffer Menu is a read-only buffer, and can be changed only through the special commands described in this section. The usual cursor motion commands can be used in this buffer. The following commands apply to the buffer described on the current line:  d Flag the buffer for deletion (killing), then move point to the next line (Buffer-menu-delete). The deletion flag is indicated by the character 'D' on the line, before the buffer name. The deletion occurs only when you type the x command (see below). C-d Like d, but move point up instead of down (Buffer-menu-delete-backwards). s Flag the buffer for saving (Buffer-menu-save). The save flag is indicated by the character 'S' on the line, before the buffer name. The saving occurs only when you type x. You may request both saving and deletion for the same buffer. x Perform all flagged deletions and saves (Buffer-menu-execute). u Remove all flags from the current line, and move down (Buffer-menu-unmark). Move to the previous line and remove all flags on that line (Buffer-menu-backup-unmark). The commands for adding or removing flags, d, C-d, s and u, all accept a numeric argument as a repeat count. The following commands operate immediately on the buffer listed on the current line. They also accept a numeric argument as a repeat count.  ~ Mark the buffer as unmodified (Buffer-menu-not-modified). See Save Commands. % Toggle the buffer's read-only status (Buffer-menu-toggle-read-only). See Misc Buffer. t Visit the buffer as a tags table (Buffer-menu-visit-tags-table). See Select Tags Table. The following commands are used to select another buffer or buffers:  q Quit the Buffer Menu (quit-window). The most recent formerly visible buffer is displayed in its place. , f Select this line's buffer, replacing the *Buffer List* buffer in its window (Buffer-menu-this-window). o Select this line's buffer in another window, as if by C-x 4 b, leaving *Buffer List* visible (Buffer-menu-other-window). C-o Display this line's buffer in another window, without selecting it (Buffer-menu-switch-other-window). 1 Select this line's buffer in a full-frame window (Buffer-menu-1-window). 2 Set up two windows on the current frame, with this line's buffer selected in one, and a previously current buffer (aside from *Buffer List*) in the other (Buffer-menu-2-window). b Bury this line's buffer (Buffer-menu-bury). m Mark this line's buffer to be displayed in another window if you exit with the v command (Buffer-menu-mark). The display flag is indicated by the character '>' at the beginning of the line. (A single buffer may not have both deletion and display flags.) v Select this line's buffer, and also display in other windows any buffers flagged with the m command (Buffer-menu-select). If you have not flagged any buffers, this command is equivalent to 1. The following commands affect the entire buffer list:  S Sort the Buffer Menu entries according to their values in the column at point. With a numeric prefix argument n, sort according to the n-th column (tabulated-list-sort). T Delete, or reinsert, lines for non-file buffers Buffer-menu-toggle-files-only). This command toggles the inclusion of such buffers in the buffer list. Normally, the buffer *Buffer List* is not updated automatically when buffers are created and killed; its contents are just text. If you have created, deleted or renamed buffers, the way to update *Buffer List* to show what you have done is to type g (revert-buffer). You can make this happen regularly every auto-revert-interval seconds if you enable Auto Revert mode in this buffer, as long as it is not marked modified. Global Auto Revert mode applies to the *Buffer List* buffer only if global-auto-revert-non-file-buffers is non-nil. See global-auto-revert-non-file-buffers, for details. ## Indirect Buffers An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is a buffer analogue of a symbolic link between files.  M-x make-indirect-buffer base-buffer indirect-name Create an indirect buffer named indirect-name with base buffer base-buffer. M-x clone-indirect-buffer Create an indirect buffer that is a twin copy of the current buffer. C-x 4 c Create an indirect buffer that is a twin copy of the current buffer, and select it in another window (clone-indirect-buffer-other-window). The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. But in all other respects, the indirect buffer and its base buffer are completely separate. They can have different names, different values of point, different narrowing, different markers, different major modes, and different local variables. An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually works by saving the base buffer. Killing the base buffer effectively kills the indirect buffer, but killing an indirect buffer has no effect on its base buffer. One way to use indirect buffers is to display multiple views of an outline. See Outline Views. A quick and handy way to make an indirect buffer is with the command M-x clone-indirect-buffer. It creates and selects an indirect buffer whose base buffer is the current buffer. With a numeric argument, it prompts for the name of the indirect buffer; otherwise it uses the name of the current buffer, with a '<n>' suffix added. C-x 4 c (clone-indirect-buffer-other-window) works like M-x clone-indirect-buffer, but it selects the new buffer in another window. These functions run the hook clone-indirect-buffer-hook after creating the indirect buffer. The more general way to make an indirect buffer is with the command M-x make-indirect-buffer. It creates an indirect buffer named indirect-name from a buffer base-buffer, prompting for both using the minibuffer. ## Convenience Features and Customization of Buffer Handling This section describes several modes and features that make it more convenient to switch between buffers. • Uniquify: Making buffer names unique with directory parts. • Iswitchb: Switching between buffers with substrings. • Buffer Menus: Configurable buffer menu. ## Making Buffer Names Unique When several buffers visit identically-named files, Emacs must give the buffers distinct names. The usual method for making buffer names unique adds '<2>', '<3>', etc. to the end of the buffer names (all but one of them). Other methods work by adding parts of each file's directory to the buffer name. To select one, load the library uniquify (e.g., using (require 'uniquify)), and customize the variable uniquify-buffer-name-style (see Easy Customization). To begin with, the forward naming method includes part of the file's directory name at the beginning of the buffer name; using this method, buffers visiting the files /u/rms/tmp/Makefile and /usr/projects/zaphod/Makefile would be named 'tmp/Makefile' and 'zaphod/Makefile', respectively (instead of 'Makefile' and 'Makefile<2>'). In contrast, the post-forward naming method would call the buffers 'Makefile|tmp' and 'Makefile|zaphod', and the reverse naming method would call them 'Makefile\tmp' and 'Makefile\zaphod'. The nontrivial difference between post-forward and reverse occurs when just one directory name is not enough to distinguish two files; then reverse puts the directory names in reverse order, so that /top/middle/file becomes 'file\middle\top', while post-forward puts them in forward order after the file name, as in 'file|top/middle'. Which rule to follow for putting the directory names in the buffer name is not very important if you are going to look at the buffer names before you type one. But as an experienced user, if you know the rule, you won't have to look. And then you may find that one rule or another is easier for you to remember and apply quickly. ## Switching Between Buffers Using Substrings Iswitchb global minor mode provides convenient switching between buffers using substrings of their names. It replaces the normal definitions of C-x b, C-x 4 b, C-x 5 b, and C-x 4 C-o with alternative commands that are somewhat "smarter". When one of these commands prompts you for a buffer name, you can type in just a substring of the name you want to choose. As you enter the substring, Iswitchb mode continuously displays a list of buffers that match the substring you have typed. At any time, you can type <RET> to select the first buffer in the list. So the way to select a particular buffer is to make it the first in the list. There are two ways to do this. You can type more of the buffer name and thus narrow down the list, excluding unwanted buffers above the desired one. Alternatively, you can use C-s and C-r to rotate the list until the desired buffer is first. <TAB> while entering the buffer name performs completion on the string you have entered, based on the displayed list of buffers. To enable Iswitchb mode, type M-x iswitchb-mode, or customize the variable iswitchb-mode to t (see Easy Customization). ## Customizing Buffer Menus  M-x bs-show Make a list of buffers similarly to M-x list-buffers but customizable. M-x bs-show pops up a buffer list similar to the one normally displayed by C-x C-b but which you can customize. If you prefer this to the usual buffer list, you can bind this command to C-x C-b. To customize this buffer list, use the bs Custom group (see Easy Customization). MSB global minor mode ("MSB" stands for "mouse select buffer") provides a different and customizable mouse buffer menu which you may prefer. It replaces the bindings of mouse-buffer-menu, normally on C-Down-Mouse-1, and the menu bar buffer menu. You can customize the menu in the msb Custom group. ## Multiple Windows Emacs can split a frame into two or many windows. Multiple windows can display parts of different buffers, or different parts of one buffer. Multiple frames always imply multiple windows, because each frame has its own set of windows. Each window belongs to one and only one frame. ## Concepts of Emacs Windows Each Emacs window displays one Emacs buffer at any time. A single buffer may appear in more than one window; if it does, any changes in its text are displayed in all the windows where it appears. But these windows can show different parts of the buffer, because each window has its own value of point. At any time, one Emacs window is the selected window; the buffer this window is displaying is the current buffer. On graphical displays, the point is indicated by a solid blinking cursor in the selected window, and by a hollow box in non-selected windows. On text terminals, the cursor is drawn only in the selected window. See Cursor Display. Commands to move point affect the value of point for the selected Emacs window only. They do not change the value of point in other Emacs windows, even those showing the same buffer. The same is true for buffer-switching commands such as C-x b; they do not affect other windows at all. However, there are other commands such as C-x 4 b that select a different window and switch buffers in it. Also, all commands that display information in a window, including (for example) C-h f (describe-function) and C-x C-b (list-buffers), work by switching buffers in a nonselected window without affecting the selected window. When multiple windows show the same buffer, they can have different regions, because they can have different values of point. However, they all have the same value for the mark, because each buffer has only one mark position. Each window has its own mode line, which displays the buffer name, modification status and major and minor modes of the buffer that is displayed in the window. The selected window's mode line appears in a different color. See Mode Line, for details. ## Splitting Windows  C-x 2 Split the selected window into two windows, one above the other (split-window-below). C-x 3 Split the selected window into two windows, positioned side by side (split-window-right). C-Mouse-2 In the mode line of a window, split that window. C-x 2 (split-window-below) splits the selected window into two windows, one above the other. After splitting, the selected window is the upper one, and the newly split-off window is below. Both windows have the same value of point as before, and display the same portion of the buffer (or as close to it as possible). If necessary, the windows are scrolled to keep point on-screen. By default, the two windows each get half the height of the original window. A positive numeric argument specifies how many lines to give to the top window; a negative numeric argument specifies how many lines to give to the bottom window. If you change the variable split-window-keep-point to nil, C-x 2 instead adjusts the portion of the buffer displayed by the two windows, as well as the value of point in each window, to keep the text on the screen as close as possible to what it was before; furthermore, if point was in the lower half of the original window, the bottom window is selected instead of the upper one. C-x 3 (split-window-right) splits the selected window into two side-by-side windows. The left window is the selected one; the right window displays the same portion of the same buffer, and has the same value of point. A positive numeric argument specifies how many columns to give the left window; a negative numeric argument specifies how many columns to give the right window. When you split a window with C-x 3, each resulting window occupies less than the full width of the frame. If it becomes too narrow, the buffer may be difficult to read if continuation lines are in use (see Continuation Lines). Therefore, Emacs automatically switches to line truncation if the window width becomes narrower than 50 columns. This truncation occurs regardless of the value of the variable truncate-lines (see Line Truncation); it is instead controlled by the variable truncate-partial-width-windows. If the value of this variable is a positive integer (the default is 50), that specifies the minimum width for a partial-width window before automatic line truncation occurs; if the value is nil, automatic line truncation is disabled; and for any other non-nil value, Emacs truncates lines in every partial-width window regardless of its width. On text terminals, side-by-side windows are separated by a vertical divider which is drawn using the vertical-border face. If you click C-Mouse-2 in the mode line of a window, that splits the window, putting a vertical divider where you click. Depending on how Emacs is compiled, you can also split a window by clicking C-Mouse-2 in the scroll bar, which puts a horizontal divider where you click (this feature does not work when Emacs uses GTK+ scroll bars). ## Using Other Windows  C-x o Select another window (other-window). C-M-v Scroll the next window (scroll-other-window). Mouse-1 Mouse-1, in the text area of a window, selects the window and moves point to the position clicked. Clicking in the mode line selects the window without moving point in it. With the keyboard, you can switch windows by typing C-x o (other-window). That is an o, for "other", not a zero. When there are more than two windows, this command moves through all the windows in a cyclic order, generally top to bottom and left to right. After the rightmost and bottommost window, it goes back to the one at the upper left corner. A numeric argument means to move several steps in the cyclic order of windows. A negative argument moves around the cycle in the opposite order. When the minibuffer is active, the minibuffer is the last window in the cycle; you can switch from the minibuffer window to one of the other windows, and later switch back and finish supplying the minibuffer argument that is requested. See Minibuffer Edit. The usual scrolling commands (see Display) apply to the selected window only, but there is one command to scroll the next window. C-M-v (scroll-other-window) scrolls the window that C-x o would select. It takes arguments, positive and negative, like C-v. (In the minibuffer, C-M-v scrolls the help window associated with the minibuffer, if any, rather than the next window in the standard cyclic order; see Minibuffer Edit.) If you set mouse-autoselect-window to a non-nil value, moving the mouse over a different window selects that window. This feature is off by default. ## Displaying in Another Window C-x 4 is a prefix key for a variety of commands that switch to a buffer in a different window—either another existing window, or a new window created by splitting the selected window. See Window Choice, for how Emacs picks or creates the window to use.  C-x 4 b bufname Select buffer bufname in another window (switch-to-buffer-other-window). C-x 4 C-o bufname Display buffer bufname in some window, without trying to select it (display-buffer). See Displaying Buffers, for details about how the window is chosen. C-x 4 f filename Visit file filename and select its buffer in another window (find-file-other-window). See Visiting. C-x 4 d directory Select a Dired buffer for directory directory in another window (dired-other-window). See Dired. C-x 4 m Start composing a mail message, similar to C-x m (see Sending Mail), but in another window (mail-other-window). C-x 4 . Find a tag in the current tags table, similar to M-. (see Tags), but in another window (find-tag-other-window). C-x 4 r filename Visit file filename read-only, and select its buffer in another window (find-file-read-only-other-window). See Visiting. ## Deleting and Rearranging Windows  C-x 0 Delete the selected window (delete-window). C-x 1 Delete all windows in the selected frame except the selected window (delete-other-windows). C-x 4 0 Delete the selected window and kill the buffer that was showing in it (kill-buffer-and-window). The last character in this key sequence is a zero. C-x ^ Make selected window taller (enlarge-window). C-x } Make selected window wider (enlarge-window-horizontally). C-x { Make selected window narrower (shrink-window-horizontally). C-x - Shrink this window if its buffer doesn't need so many lines (shrink-window-if-larger-than-buffer). C-x + Make all windows the same height (balance-windows). To delete the selected window, type C-x 0 (delete-window). Once a window is deleted, the space that it occupied is given to an adjacent window (but not the minibuffer window, even if that is active at the time). Deleting the window has no effect on the buffer it used to display; the buffer continues to exist, and you can still switch to with C-x b. C-x 4 0 (kill-buffer-and-window) is a stronger command than C-x 0; it kills the current buffer and then deletes the selected window. C-x 1 (delete-other-windows) deletes all the windows, except the selected one; the selected window expands to use the whole frame. (This command cannot be used while the minibuffer window is active; attempting to do so signals an error.) The command C-x ^ (enlarge-window) makes the selected window one line taller, taking space from a vertically adjacent window without changing the height of the frame. With a positive numeric argument, this command increases the window height by that many lines; with a negative argument, it reduces the height by that many lines. If there are no vertically adjacent windows (i.e., the window is at the full frame height), that signals an error. The command also signals an error if you attempt to reduce the height of any window below a certain minimum number of lines, specified by the variable window-min-height (the default is 4). Similarly, C-x } (enlarge-window-horizontally) makes the selected window wider, and C-x { (shrink-window-horizontally) makes it narrower. These commands signal an error if you attempt to reduce the width of any window below a certain minimum number of columns, specified by the variable window-min-width (the default is 10). C-x - (shrink-window-if-larger-than-buffer) reduces the height of the selected window, if it is taller than necessary to show the whole text of the buffer it is displaying. It gives the extra lines to other windows in the frame. You can also use C-x + (balance-windows) to even out the heights of all the windows in the selected frame. Mouse clicks on the mode line provide another way to change window heights and to delete windows. See Mode Line Mouse. ## Displaying A Buffer In A Window It is a common Emacs operation to display or "pop up" some buffer in response to a user command. There are different ways in which commands do this. Many commands, like C-x C-f (find-file), display the buffer by "taking over" the selected window, expecting that the user's attention will be diverted to that buffer. These commands usually work by calling switch-to-buffer internally (see Select Buffer). Some commands try to display "intelligently", trying not to take over the selected window, e.g., by splitting off a new window and displaying the desired buffer there. Such commands, which include the various help commands (see Help), work by calling display-buffer internally. See Window Choice, for details. Other commands do the same as display-buffer, and additionally select the displaying window so that you can begin editing its buffer. The command C-x  (next-error) is one example (see Compilation Mode). Such commands work by calling the function pop-to-buffer internally. Commands with names ending in -other-window behave like display-buffer, except that they never display in the selected window. Several of these commands are bound in the C-x 4 prefix key (see Pop Up Window). Commands with names ending in -other-frame behave like display-buffer, except that they (1) never display in the selected window and (2) prefer to create a new frame to display the desired buffer instead of splitting a window—as though the variable pop-up-frames is set to t (see Window Choice). Several of these commands are bound in the C-x 5 prefix key. ## How display-buffer Works The display-buffer command (as well as commands that call it internally) chooses a window to display by following the steps given below. • First, check if the buffer should be displayed in the selected window regardless of other considerations. You can tell Emacs to do this by adding the desired buffer's name to the list same-window-buffer-names, or adding a matching regular expression to the list same-window-regexps. By default, these variables are nil, so this step is skipped. • Otherwise, if the buffer is already displayed in an existing window, "reuse" that window. Normally, only windows on the selected frame are considered, but windows on other frames are also reusable if you change pop-up-frames (see below) to t. • Otherwise, optionally create a new frame and display the buffer there. By default, this step is skipped. To enable it, change the variable pop-up-frames to a non-nil value. The special value graphic-only means to do this only on graphical displays. • Otherwise, try to create a new window by splitting the selected window, and display the buffer in that new window. The split can be either vertical or horizontal, depending on the variables split-height-threshold and split-width-threshold. These variables should have integer values. If split-height-threshold is smaller than the selected window's height, the split puts the new window below. Otherwise, if split-width-threshold is smaller than the window's width, the split puts the new window on the right. If neither condition holds, Emacs tries to split so that the new window is below—but only if the window was not split before (to avoid excessive splitting). • Otherwise, display the buffer in an existing window on the selected frame. • If all the above methods fail for whatever reason, create a new frame and display the buffer there. ## Convenience Features for Window Handling Winner mode is a global minor mode that records the changes in the window configuration (i.e., how the frames are partitioned into windows), so that you can "undo" them. You can toggle Winner mode with M-x winner-mode, or by customizing the variable winner-mode. When the mode is enabled, C-c left (winner-undo) undoes the last window configuration change. If you change your mind while undoing, you can redo the changes you had undone using C-c right (M-x winner-redo). Follow mode (M-x follow-mode) synchronizes several windows on the same buffer so that they always display adjacent sections of that buffer. See Follow Mode. The Windmove package defines commands for moving directionally between neighboring windows in a frame. M-x windmove-right selects the window immediately to the right of the currently selected one, and similarly for the "left", "up", and "down" counterparts. M-x windmove-default-keybindings binds these commands to S-right etc.; doing so disables shift selection for those keys (see Shift Selection). The command M-x compare-windows lets you compare the text shown in different windows. See Comparing Files. Scroll All mode (M-x scroll-all-mode) is a global minor mode that causes scrolling commands and point motion commands to apply to every single window. ## Frames and Graphical Displays When Emacs is started on a graphical display, e.g., on the X Window System, it occupies a graphical system-level "window". In this manual, we call this a frame, reserving the word "window" for the part of the frame used for displaying a buffer. A frame initially contains one window, but it can be subdivided into multiple windows (see Windows). A frame normally also contains a menu bar, tool bar, and echo area. You can also create additional frames (see Creating Frames). All frames created in the same Emacs session have access to the same underlying buffers and other data. For instance, if a buffer is being shown in more than one frame, any changes made to it in one frame show up immediately in the other frames too. Typing C-x C-c closes all the frames on the current display, and ends the Emacs session if it has no frames open on any other displays (see Exiting). To close just the selected frame, type C-x 5 0. This chapter describes Emacs features specific to graphical displays (particularly mouse commands), and features for managing multiple frames. On text terminals, many of these features are unavailable. However, it is still possible to create multiple "frames" on text terminals; such frames are displayed one at a time, filling the entire terminal screen (see Non-Window Terminals). It is also possible to use the mouse on some text terminals (see Text-Only Mouse, for doing so on GNU and Unix systems). ## Mouse Commands for Words and Lines  Mouse-1 Move point to where you click (mouse-set-point). Drag-Mouse-1 Activate the region around the text selected by dragging, and put the text in the primary selection (mouse-set-region). Mouse-2 Move point to where you click, and insert the contents of the primary selection there (mouse-yank-primary). Mouse-3 If the region is active, move the nearer end of the region to the click position; otherwise, set mark at the current value of point and point at the click position. Save the resulting region in the kill ring; on a second click, kill it (mouse-save-then-kill). The most basic mouse command is mouse-set-point, which is invoked by clicking with the left mouse button, Mouse-1, in the text area of a window. This moves point to the position where you clicked. If that window was not the selected window, it becomes the selected window. Normally, if the frame you clicked in was not the selected frame, it is made the selected frame, in addition to selecting the window and setting the cursor. On the X Window System, you can change this by setting the variable x-mouse-click-focus-ignore-position to t. In that case, the initial click on an unselected frame just selects the frame, without doing anything else; clicking again selects the window and sets the cursor position. Holding down Mouse-1 and "dragging" the mouse over a stretch of text activates the region around that text (mouse-set-region), placing the mark where you started holding down the mouse button, and point where you release it (see Mark). Also, the text in the region becomes the primary selection (see Primary Selection). If you change the variable mouse-drag-copy-region to a non-nil value, dragging the mouse over a stretch of text also adds the text to the kill ring. The default is nil. If you move the mouse off the top or bottom of the window while dragging, the window scrolls at a steady rate until you move the mouse back into the window. This way, you can select regions that don't fit entirely on the screen. The number of lines scrolled per step depends on how far away from the window edge the mouse has gone; the variable mouse-scroll-min-lines specifies a minimum step size. Clicking with the middle mouse button, Mouse-2, moves point to the position where you clicked and inserts the contents of the primary selection (mouse-yank-primary). See Primary Selection. This behavior is consistent with other X applications. Alternatively, you can rebind Mouse-2 to mouse-yank-at-click, which performs a yank at point. If you change the variable mouse-yank-at-point to a non-nil value, Mouse-2 does not move point; it inserts the text at point, regardless of where you clicked or even which of the frame's windows you clicked on. This variable affects both mouse-yank-primary and mouse-yank-at-click. Clicking with the right mouse button, Mouse-3, runs the command mouse-save-then-kill. This performs several actions depending on where you click and the status of the region: • If no region is active, clicking Mouse-3 activates the region, placing the mark where point was and point at the clicked position. • If a region is active, clicking Mouse-3 adjusts the nearer end of the region by moving it to the clicked position. The adjusted region's text is copied to the kill ring; if the text in the original region was already on the kill ring, it replaces it there. • If you originally specified the region using a double or triple Mouse-1, so that the region is defined to consist of entire words or lines (see Word and Line Mouse), then adjusting the region with Mouse-3 also proceeds by entire words or lines. • If you use Mouse-3 a second time consecutively, at the same place, that kills the region already selected. Thus, the simplest way to kill text with the mouse is to click Mouse-1 at one end, then click Mouse-3 twice at the other end. To copy the text into the kill ring without deleting it from the buffer, press Mouse-3 just once—or just drag across the text with Mouse-1. Then you can copy it elsewhere by yanking it. The mouse-save-then-kill command also obeys the variable mouse-drag-copy-region (described above). If the value is non-nil, then whenever the command sets or adjusts the active region, the text in the region is also added to the kill ring. If the latest kill ring entry had been added the same way, that entry is replaced rather than making a new entry. Whenever you set the region using any of the mouse commands described above, the mark will be deactivated by any subsequent unshifted cursor motion command, in addition to the usual ways of deactivating the mark. See Shift Selection. Some mice have a "wheel" which can be used for scrolling. Emacs supports scrolling windows with the mouse wheel, by default, on most graphical displays. To toggle this feature, use M-x mouse-wheel-mode. The variables mouse-wheel-follow-mouse and mouse-wheel-scroll-amount determine where and by how much buffers are scrolled. The variable mouse-wheel-progressive-speed determines whether the scroll speed is linked to how fast you move the wheel. ## Mouse Commands for Words and Lines These variants of Mouse-1 select entire words or lines at a time. Emacs activates the region around the selected text, which is also copied to the kill ring.  Double-Mouse-1 Select the text around the word which you click on. Double-clicking on a character with "symbol" syntax (such as underscore, in C mode) selects the symbol surrounding that character. Double-clicking on a character with open- or close-parenthesis syntax selects the parenthetical grouping which that character starts or ends. Double-clicking on a character with string-delimiter syntax (such as a single-quote or double-quote in C) selects the string constant (Emacs uses heuristics to figure out whether that character is the beginning or the end of it). Double-Drag-Mouse-1 Select the text you drag across, in the form of whole words. Triple-Mouse-1 Select the line you click on. Triple-Drag-Mouse-1 Select the text you drag across, in the form of whole lines. ## Following References with the Mouse Some Emacs buffers include buttons, or hyperlinks: pieces of text that perform some action (e.g., following a reference) when activated (e.g., by clicking on them). Usually, a button's text is visually highlighted: it is underlined, or a box is drawn around it. If you move the mouse over a button, the shape of the mouse cursor changes and the button lights up. If you change the variable mouse-highlight to nil, Emacs disables this highlighting. You can activate a button by moving point to it and typing <RET>, or by clicking either Mouse-1 or Mouse-2 on the button. For example, in a Dired buffer, each file name is a button; activating it causes Emacs to visit that file (see Dired). In a *Compilation* buffer, each error message is a button, and activating it visits the source code for that error (see Compilation). Although clicking Mouse-1 on a button usually activates the button, if you hold the mouse button down for a period of time before releasing it (specifically, for more than 450 milliseconds), then Emacs moves point where you clicked, without activating the button. In this way, you can use the mouse to move point over a button without activating it. Dragging the mouse over or onto a button has its usual behavior of setting the region, and does not activate the button. You can change how Mouse-1 applies to buttons by customizing the variable mouse-1-click-follows-link. If the value is a positive integer, that determines how long you need to hold the mouse button down for, in milliseconds, to cancel button activation; the default is 450, as described in the previous paragraph. If the value is nil, Mouse-1 just sets point where you clicked, and does not activate buttons. If the value is double, double clicks activate buttons but single clicks just set point. Normally, Mouse-1 on a button activates the button even if it is in a non-selected window. If you change the variable mouse-1-click-in-non-selected-windows to nil, Mouse-1 on a button in an unselected window moves point to the clicked position and selects that window, without activating the button. Several mouse clicks with the <Ctrl> and <SHIFT> modifiers bring up menus.  C-Mouse-1 This menu is for selecting a buffer. The MSB ("mouse select buffer") global minor mode makes this menu smarter and more customizable. See Buffer Menus. C-Mouse-2 This menu contains entries for examining faces and other text properties, and well as for setting them (the latter is mainly useful when editing enriched text; see Enriched Text). C-Mouse-3 This menu is mode-specific. For most modes if Menu-bar mode is on, this menu has the same items as all the mode-specific menu-bar menus put together. Some modes may specify a different menu for this button. If Menu Bar mode is off, this menu contains all the items which would be present in the menu bar—not just the mode-specific ones—so that you can access them without having to display the menu bar. S-Mouse-1 This menu is for changing the default face within the window's buffer. See Text Scale. Some graphical applications use Mouse-3 for a mode-specific menu. If you prefer Mouse-3 in Emacs to bring up such a menu instead of running the mouse-save-then-kill command, rebind Mouse-3 by adding the following line to your init file (see Init Rebinding): (global-set-key [mouse-3] 'mouse-popup-menubar-stuff)  ## Mode Line Mouse Commands You can use mouse clicks on window mode lines to select and manipulate windows. Some areas of the mode line, such as the buffer name, and major and minor mode names, have their own special mouse bindings. These areas are highlighted when you hold the mouse over them, and information about the special bindings will be displayed (see Tooltips). This section's commands do not apply in those areas.  Mouse-1 Mouse-1 on a mode line selects the window it belongs to. By dragging Mouse-1 on the mode line, you can move it, thus changing the height of the windows above and below. Changing heights with the mouse in this way never deletes windows, it just refuses to make any window smaller than the minimum height. Mouse-2 Mouse-2 on a mode line expands that window to fill its frame. Mouse-3 Mouse-3 on a mode line deletes the window it belongs to. If the frame has only one window, it does nothing. C-Mouse-2 C-Mouse-2 on a mode line splits that window, producing two side-by-side windows with the boundary running through the click position (see Split Window). Furthermore, by clicking and dragging Mouse-1 on the divider between two side-by-side mode lines, you can move the vertical boundary to the left or right. ## Creating Frames The prefix key C-x 5 is analogous to C-x 4. Whereas each C-x 4 command pops up a buffer in a different window in the selected frame (see Pop Up Window), the C-x 5 commands use a different frame. If an existing visible or iconified ("minimized") frame already displays the requested buffer, that frame is raised and deiconified ("un-minimized"); otherwise, a new frame is created on the current display terminal. The various C-x 5 commands differ in how they find or create the buffer to select:  C-x 5 2 Create a new frame (make-frame-command). C-x 5 b bufname Select buffer bufname in another frame. This runs switch-to-buffer-other-frame. C-x 5 f filename Visit file filename and select its buffer in another frame. This runs find-file-other-frame. See Visiting. C-x 5 d directory Select a Dired buffer for directory directory in another frame. This runs dired-other-frame. See Dired. C-x 5 m Start composing a mail message in another frame. This runs mail-other-frame. It is the other-frame variant of C-x m. See Sending Mail. C-x 5 . Find a tag in the current tag table in another frame. This runs find-tag-other-frame, the multiple-frame variant of M-.. See Tags. C-x 5 r filename Visit file filename read-only, and select its buffer in another frame. This runs find-file-read-only-other-frame. See Visiting. You can control the appearance and behavior of the newly-created frames by specifying frame parameters. See Frame Parameters. ## Frame Commands The following commands are used to delete and operate on frames:  C-x 5 0 Delete the selected frame (delete-frame). This signals an error if there is only one frame. C-z Minimize (or "iconify) the selected Emacs frame (suspend-frame). See Exiting. C-x 5 o Select another frame, and raise it. If you repeat this command, it cycles through all the frames on your terminal. C-x 5 1 Delete all frames on the current terminal, except the selected one. The C-x 5 0 (delete-frame) command deletes the selected frame. However, it will refuse to delete the last frame in an Emacs session, to prevent you from losing the ability to interact with the Emacs session. Note that when Emacs is run as a daemon (see Emacs Server), there is always a "virtual frame" that remains after all the ordinary, interactive frames are deleted. In this case, C-x 5 0 can delete the last interactive frame; you can use emacsclient to reconnect to the Emacs session. The C-x 5 1 (delete-other-frames) command deletes all other frames on the current terminal (this terminal refers to either a graphical display, or a text terminal; see Non-Window Terminals). If the Emacs session has frames open on other graphical displays or text terminals, those are not deleted. The C-x 5 o (other-frame) command selects the next frame on the current terminal. If you are using Emacs on the X Window System with a window manager that selects (or gives focus to) whatever frame the mouse cursor is over, you have to change the variable focus-follows-mouse to t in order for this command to work properly. Then invoking C-x 5 o will also warp the mouse cursor to the chosen frame. ## Fonts By default, Emacs displays text on graphical displays using a 12-point monospace font. There are different ways to specify a different font: • Click on 'Set Default Font' in the 'Options' menu. To save this for future sessions, click on 'Save Options' in the 'Options' menu. • Add a line to your init file, modifying the variable default-frame-alist to specify the font parameter (see Frame Parameters), like this: (add-to-list 'default-frame-alist '(font . "DejaVu Sans Mono-10"))  • Add an 'emacs.font' X resource setting to your X resource file, like this: emacs.font: DejaVu Sans Mono-12  You must restart X, or use the xrdb command, for the X resources file to take effect. See Resources. Do not quote font names in X resource files. • If you are running Emacs on the GNOME desktop, you can tell Emacs to use the default system font by setting the variable font-use-system-font to t (the default is nil). For this to work, Emacs must have been compiled with Gconf support. • Use the command line option '-fn' (or '--font'). See Font X. To check what font you're currently using, the C-u C-x = command can be helpful. It describes the character at point, and names the font that it's rendered in. On X, there are four different ways to express a "font name". The first is to use a Fontconfig pattern. Fontconfig patterns have the following form: fontname[-fontsize][:name1=values1][:name2=values2]...  Within this format, any of the elements in braces may be omitted. Here, fontname is the family name of the font, such as 'Monospace' or 'DejaVu Sans Mono'; fontsize is the point size of the font (one printer's point is about 1/72 of an inch); and the 'name=values' entries specify settings such as the slant and weight of the font. Each values may be a single value, or a list of values separated by commas. Also, some property values are valid with only one kind of property name, in which case the 'name=' part may be omitted. Here is a list of common font properties:  'slant' One of 'italic', 'oblique', or 'roman'. 'weight' One of 'light', 'medium', 'demibold', 'bold' or 'black'. 'style' Some fonts define special styles which are a combination of slant and weight. For instance, 'Dejavu Sans' defines the 'book' style, which overrides the slant and weight properties. 'width' One of 'condensed', 'normal', or 'expanded'. 'spacing' One of 'monospace', 'proportional', 'dual-width', or 'charcell'. Here are some examples of Fontconfig patterns: Monospace Monospace-12 Monospace-12:bold DejaVu Sans Mono:bold:italic Monospace-12:weight=bold:slant=italic For a more detailed description of Fontconfig patterns, see the Fontconfig manual, which is distributed with Fontconfig and available online at https://www.freedesktop.org/software/fontconfig/fontconfig-user.html. The second way to specify a font is to use a GTK font pattern. These have the syntax fontname [properties] [fontsize]  where fontname is the family name, properties is a list of property values separated by spaces, and fontsize is the point size. The properties that you may specify for GTK font patterns are as follows: • Slant properties: 'Italic' or 'Oblique'. If omitted, the default (roman) slant is implied. • Weight properties: 'Bold', 'Book', 'Light', 'Medium', 'Semi-bold', or 'Ultra-light'. If omitted, 'Medium' weight is implied. • Width properties: 'Semi-Condensed' or 'Condensed'. If omitted, a default width is used. Here are some examples of GTK font patterns: • Monospace 12 • Monospace Bold Italic 12 The third way to specify a font is to use an XLFD (X Logical Font Description). This is the traditional method for specifying fonts under X. Each XLFD consists of fourteen words or numbers, separated by dashes, like this: -misc-fixed-medium-r-semicondensed--13-*-*-*-c-60-iso8859-1  A wildcard character ('*') in an XLFD matches any sequence of characters (including none), and '?' matches any single character. However, matching is implementation-dependent, and can be inaccurate when wildcards match dashes in a long name. For reliable results, supply all 14 dashes and use wildcards only within a field. Case is insignificant in an XLFD. The syntax for an XLFD is as follows: -maker-family-weight-slant-widthtype-style... ...-pixels-height-horiz-vert-spacing-width-registry-encoding The entries have the following meanings:  maker The name of the font manufacturer. family The name of the font family (e.g., 'courier'). weight The font weight; normally either 'bold', 'medium' or 'light'. Some font names support other values. slant The font slant; normally 'r' (roman), 'i' (italic), 'o' (oblique), 'ri' (reverse italic), or 'ot' (other). Some font names support other values. widthtype The font width; normally 'normal', 'condensed', 'semicondensed', or 'extended'. Some font names support other values. style An optional additional style name. Usually it is empty; most XLFDs have two hyphens in a row at this point. pixels The font height, in pixels. height The font height on the screen, measured in tenths of a printer's point. This is the point size of the font, times ten. For a given vertical resolution, height and pixels are proportional; therefore, it is common to specify just one of them and use '*' for the other. horiz The horizontal resolution, in pixels per inch, of the screen for which the font is intended. vert The vertical resolution, in pixels per inch, of the screen for which the font is intended. Normally the resolution of the fonts on your system is the right value for your screen; therefore, you normally specify '*' for this and horiz. spacing This is 'm' (monospace), 'p' (proportional) or 'c' (character cell). width The average character width, in pixels, multiplied by ten. registry, encoding The X font character set that the font depicts. (X font character sets are not the same as Emacs character sets, but they are similar.) You can use the xfontsel program to check which choices you have. Normally you should use 'iso8859' for Registry and '1' for encoding. The fourth and final method of specifying a font is to use a "font nickname". Certain fonts have shorter nicknames, which you can use instead of a normal font specification. For instance, '6x13' is equivalent to -misc-fixed-medium-r-semicondensed--13-*-*-*-c-60-iso8859-1  On X, Emacs recognizes two types of fonts: client-side fonts, which are provided by the Xft and Fontconfig libraries, and server-side fonts, which are provided by the X server itself. Most client-side fonts support advanced font features such as antialiasing and subpixel hinting, while server-side fonts do not. Fontconfig and GTK patterns match only client-side fonts. You will probably want to use a fixed-width default font—that is, a font in which all characters have the same width. For Xft and Fontconfig fonts, you can use the fc-list command to list the available fixed-width fonts, like this: fc-list :spacing=mono fc-list :spacing=charcell For server-side X fonts, you can use the xlsfonts program to list the available fixed-width fonts, like this: xlsfonts -fn '*x*' | egrep "^[0-9]+x[0-9]+" xlsfonts -fn '*-*-*-*-*-*-*-*-*-*-*-m*' xlsfonts -fn '*-*-*-*-*-*-*-*-*-*-*-c*' Any font with 'm' or 'c' in the spacing field of the XLFD is a fixed-width font. To see what a particular font looks like, use the xfd command. For example: xfd -fn 6x13  displays the entire font '6x13'. While running Emacs, you can also set the font of a specific kind of text (see Faces), or a particular frame (see Frame Parameters). ## Speedbar Frames The speedbar is a special frame for conveniently navigating in or operating on another frame. The speedbar, when it exists, is always associated with a specific frame, called its attached frame; all speedbar operations act on that frame. Type M-x speedbar to create the speedbar and associate it with the current frame. To dismiss the speedbar, type M-x speedbar again, or select the speedbar and type q. (You can also delete the speedbar frame like any other Emacs frame.) If you wish to associate the speedbar with a different frame, dismiss it and call M-x speedbar from that frame. The speedbar can operate in various modes. Its default mode is File Display mode, which shows the files in the current directory of the selected window of the attached frame, one file per line. Clicking on a file name visits that file in the selected window of the attached frame, and clicking on a directory name shows that directory in the speedbar (see Mouse References). Each line also has a box, '[+]' or '<+>', that you can click on to expand the contents of that item. Expanding a directory adds the contents of that directory to the speedbar display, underneath the directory's own line. Expanding an ordinary file adds a list of the tags in that file to the speedbar display; you can click on a tag name to jump to that tag in the selected window of the attached frame. When a file or directory is expanded, the '[+]' changes to '[-]'; you can click on that box to contract the item, hiding its contents. You navigate through the speedbar using the keyboard, too. Typing <RET> while point is on a line in the speedbar is equivalent to clicking the item on the current line, and <SPC> expands or contracts the item. U displays the parent directory of the current directory. To copy, delete, or rename the file on the current line, type C, D, and R respectively. To create a new directory, type M. Another general-purpose speedbar mode is Buffer Display mode; in this mode, the speedbar displays a list of Emacs buffers. To switch to this mode, type b in the speedbar. To return to File Display mode, type f. You can also change the display mode by clicking mouse-3 anywhere in the speedbar window (or mouse-1 on the mode-line) and selecting 'Displays' in the pop-up menu. Some major modes, including Rmail mode, Info, and GUD, have specialized ways of putting useful items into the speedbar for you to select. For example, in Rmail mode, the speedbar shows a list of Rmail files, and lets you move the current message to another Rmail file by clicking on its '<M>' box. For more details on using and programming the speedbar, See Speedbar. ## Multiple Displays A single Emacs can talk to more than one X display. Initially, Emacs uses just one display—the one specified with the DISPLAY environment variable or with the '--display' option (see Options). To connect to another display, use the command make-frame-on-display:  M-x make-frame-on-display display Create a new frame on display display. A single X server can handle more than one screen. When you open frames on two screens belonging to one server, Emacs knows they share a single keyboard, and it treats all the commands arriving from these screens as a single stream of input. When you open frames on different X servers, Emacs makes a separate input stream for each server. Each server also has its own selected frame. The commands you enter with a particular X server apply to that server's selected frame. ## Frame Parameters You can control the default appearance and behavior of all frames by specifying a default list of frame parameters in the variable default-frame-alist. Its value should be a list of entries, each specifying a parameter name and a value for that parameter. These entries take effect whenever Emacs creates a new frame, including the initial frame. For example, you can add the following lines to your init file (see Init File) to set the default frame width to 90 character columns, the default frame height to 40 character rows, and the default font to 'Monospace-10': (add-to-list 'default-frame-alist '(width . 90)) (add-to-list 'default-frame-alist '(height . 40)) (add-to-list 'default-frame-alist '(font . "Monospace-10"))  You can also specify a list of frame parameters which apply to just the initial frame, by customizing the variable initial-frame-alist. If Emacs is compiled to use an X toolkit, frame parameters that specify colors and fonts don't affect menus and the menu bar, since those are drawn by the toolkit and not directly by Emacs. ## Scroll Bars On graphical displays, there is a scroll bar on the side of each Emacs window. Clicking Mouse-1 on the scroll bar's up and down buttons scrolls the window by one line at a time. Clicking Mouse-1 above or below the scroll bar's inner box scrolls the window by nearly the entire height of the window, like M-v and C-v respectively (see Moving Point). Dragging the inner box scrolls continuously. If Emacs is compiled on the X Window System without X toolkit support, the scroll bar behaves differently. Clicking Mouse-1 anywhere on the scroll bar scrolls forward like C-v, while Mouse-3 scrolls backward like M-v. Clicking Mouse-2 in the scroll bar lets you drag the inner box up and down. To toggle the use of scroll bars, type M-x scroll-bar-mode. This command applies to all frames, including frames yet to be created. To toggle scroll bars for just the selected frame, use the command M-x toggle-scroll-bar. To control the use of scroll bars at startup, customize the variable scroll-bar-mode. Its value should be either right (put scroll bars on the right side of windows), left (put them on the left), or nil (disable scroll bars). By default, Emacs puts scroll bars on the right if it was compiled with GTK+ support on the X Window System, and on MS Windows or Mac OS; Emacs puts scroll bars on the left if compiled on the X Window System without GTK+ support (following the old convention for X applications). You can also use the X resource 'verticalScrollBars' to enable or disable the scroll bars (see Resources). To control the scroll bar width, change the scroll-bar-width frame parameter (see Frame Parameters). ## Drag and Drop In most graphical desktop environments, Emacs has basic support for drag and drop operations. For instance, dropping text onto an Emacs frame inserts the text where it is dropped. Dropping a file onto an Emacs frame visits that file. As a special case, dropping the file on a Dired buffer moves or copies the file (according to the conventions of the application it came from) into the directory displayed in that buffer. Dropping a file normally visits it in the window you drop it on. If you prefer to visit the file in a new window in such cases, customize the variable dnd-open-file-other-window. The XDND and Motif drag and drop protocols, and the old KDE 1.x protocol, are currently supported. You can toggle the use of menu bars with M-x menu-bar-mode. With no argument, this command toggles Menu Bar mode, a global minor mode. With an argument, the command turns Menu Bar mode on if the argument is positive, off if the argument is not positive. To control the use of menu bars at startup, customize the variable menu-bar-mode. Expert users often turn off the menu bar, especially on text terminals, where this makes one additional line available for text. If the menu bar is off, you can still pop up a menu of its contents with C-Mouse-3 on a display which supports pop-up menus. See Menu Mouse Clicks. See Menu Bar, for information on how to invoke commands with the menu bar. See X Resources, for how to customize the menu bar menus' visual appearance. ## Tool Bars On graphical displays, Emacs puts a tool bar at the top of each frame, just below the menu bar. This is a row of icons which you can click on with the mouse to invoke various commands. The global (default) tool bar contains general commands. Some major modes define their own tool bars; whenever a buffer with such a major mode is current, the mode's tool bar replaces the global tool bar. To toggle the use of tool bars, type M-x tool-bar-mode. This command applies to all frames, including frames yet to be created. To control the use of tool bars at startup, customize the variable tool-bar-mode. When Emacs is compiled with GTK+ support, each tool bar item can consist of an image, or a text label, or both. By default, Emacs follows the Gnome desktop's tool bar style setting; if none is defined, it displays tool bar items as just images. To impose a specific tool bar style, customize the variable tool-bar-style. You can also control the placement of the tool bar for the GTK+ tool bar with the frame parameter tool-bar-position. See Frame Parameters. ## Using Dialog Boxes A dialog box is a special kind of menu for asking you a yes-or-no question or some other special question. Many Emacs commands use a dialog box to ask a yes-or-no question, if you used the mouse to invoke the command that led to the question. To disable the use of dialog boxes, change the variable use-dialog-box to nil. In that case, Emacs always performs yes-or-no prompts using the echo area and keyboard input. This variable also controls whether to use file selection windows (but those are not supported on all platforms). A file selection window is a special kind of dialog box for asking for file names. You can customize the variable use-file-dialog to suppress the use of file selection windows, even if you still want other kinds of dialogs. This variable has no effect if you have suppressed all dialog boxes with the variable use-dialog-box. When Emacs is compiled with GTK+ support, it uses the GTK+ "file chooser" dialog. Emacs adds an additional toggle button to this dialog, which you can use to enable or disable the display of hidden files (files starting with a dot) in that dialog. If you want this toggle to be activated by default, change the variable x-gtk-show-hidden-files to t. Also, Emacs adds help text to the GTK+ file chooser dialog; to disable this help text, change the variable x-gtk-file-dialog-help-text to nil. ## Tooltips Tooltips are small windows that display text information at the current mouse position. They activate when there is a pause in mouse movement over some significant piece of text in a window, or the mode line, or some other part of the Emacs frame such as a tool bar button or menu item. You can toggle the use of tooltips with the command M-x tooltip-mode. When Tooltip mode is disabled, the help text is displayed in the echo area instead. To control the use of tooltips at startup, customize the variable tooltip-mode. The variables tooltip-delay specifies how long Emacs should wait before displaying a tooltip. For additional customization options for displaying tooltips, use M-x customize-group <RET> tooltip <RET>. If Emacs is built with GTK+ support, it displays tooltips via GTK+, using the default appearance of GTK+ tooltips. To disable this, change the variable x-gtk-use-system-tooltips to nil. If you do this, or if Emacs is built without GTK+ support, most attributes of the tooltip text are specified by the tooltip face, and by X resources (see X Resources). GUD tooltips are special tooltips that show the values of variables when debugging a program with GUD. See Debugger Operation. ## Mouse Avoidance On graphical terminals, the mouse pointer may obscure the text in the Emacs frame. Emacs provides two methods to avoid this problem. Firstly, Emacs hides the mouse pointer each time you type a self-inserting character, if the pointer lies inside an Emacs frame; moving the mouse pointer makes it visible again. To disable this feature, set the variable make-pointer-invisible to nil. Secondly, you can use Mouse Avoidance mode, a minor mode, to keep the mouse pointer away from point. To use Mouse Avoidance mode, customize the variable mouse-avoidance-mode. You can set this to various values to move the mouse in several ways:  banish Move the pointer to a corner of the frame on any key-press. You can customize the variable mouse-avoidance-banish-position to specify where the pointer goes when it is banished. exile Banish the pointer only if the cursor gets too close, and allow it to return once the cursor is out of the way. jump If the cursor gets too close to the pointer, displace the pointer by a random distance and direction. animate Like jump, but shows steps along the way for illusion of motion. cat-and-mouse The same as animate. proteus Like animate, but changes the shape of the mouse pointer too. You can also use the command M-x mouse-avoidance-mode to enable the mode. Whenever Mouse Avoidance mode moves the mouse, it also raises the frame. ## Non-Window Terminals On a text terminal, Emacs can display only one Emacs frame at a time. However, you can still create multiple Emacs frames, and switch between them. Switching frames on these terminals is much like switching between different window configurations. Use C-x 5 2 to create a new frame and switch to it; use C-x 5 o to cycle through the existing frames; use C-x 5 0 to delete the current frame. Each frame has a number to distinguish it. If your terminal can display only one frame at a time, the selected frame's number n appears near the beginning of the mode line, in the form 'Fn'. 'Fn' is in fact the frame's initial name. You can give frames more meaningful names if you wish, and you can select a frame by its name. Use the command M-x set-frame-name <RET> name <RET> to specify a new name for the selected frame, and use M-x select-frame-by-name <RET> name <RET> to select a frame according to its name. The name you specify appears in the mode line when the frame is selected. ## Using a Mouse in Text Terminals Some text terminals support mouse clicks in the terminal window. In a terminal emulator which is compatible with xterm, you can use M-x xterm-mouse-mode to give Emacs control over simple uses of the mouse; basically, only non-modified single clicks are supported. The normal xterm mouse functionality for such clicks is still available by holding down the Shift key when you press the mouse button. Xterm Mouse mode is a global minor mode (see Minor Modes). Repeating the command turns the mode off again. In the console on GNU/Linux, you can use M-x gpm-mouse-mode to enable mouse support. You must have the gpm server installed and running on your system in order for this to work. ## International Character Set Support Emacs supports a wide variety of international character sets, including European and Vietnamese variants of the Latin alphabet, as well as Cyrillic, Devanagari (for Hindi and Marathi), Ethiopic, Greek, Han (for Chinese and Japanese), Hangul (for Korean), Hebrew, IPA, Kannada, Lao, Malayalam, Tamil, Thai, Tibetan, and Vietnamese scripts. Emacs also supports various encodings of these characters that are used by other internationalized software, such as word processors and mailers. Emacs allows editing text with international characters by supporting all the related activities: • You can visit files with non-ASCII characters, save non-ASCII text, and pass non-ASCII text between Emacs and programs it invokes (such as compilers, spell-checkers, and mailers). Setting your language environment (see Language Environments) takes care of setting up the coding systems and other options for a specific language or culture. Alternatively, you can specify how Emacs should encode or decode text for each command; see Text Coding. • You can display non-ASCII characters encoded by the various scripts. This works by using appropriate fonts on graphics displays (see Defining Fontsets), and by sending special codes to text displays (see Terminal Coding). If some characters are displayed incorrectly, refer to Undisplayable Characters, which describes possible problems and explains how to solve them. • Characters from scripts whose natural ordering of text is from right to left are reordered for display (see Bidirectional Editing). These scripts include Arabic, Hebrew, Syriac, Thaana, and a few others. • You can insert non-ASCII characters or search for them. To do that, you can specify an input method (see Select Input Method) suitable for your language, or use the default input method set up when you chose your language environment. If your keyboard can produce non-ASCII characters, you can select an appropriate keyboard coding system (see Terminal Coding), and Emacs will accept those characters. Latin-1 characters can also be input by using the C-x 8 prefix, see Unibyte Mode. With the X Window System, your locale should be set to an appropriate value to make sure Emacs interprets keyboard input correctly; see locales. The rest of this chapter describes these issues in detail. ## Introduction to International Character Sets The users of international character sets and scripts have established many more-or-less standard coding systems for storing files. These coding systems are typically multibyte, meaning that sequences of two or more bytes are used to represent individual non-ASCII characters. Internally, Emacs uses its own multibyte character encoding, which is a superset of the Unicode standard. This internal encoding allows characters from almost every known script to be intermixed in a single buffer or string. Emacs translates between the multibyte character encoding and other coding systems when reading and writing files, and when exchanging data with subprocesses. The command C-h h (view-hello-file) displays the file etc/HELLO, which illustrates various scripts by showing how to say "hello" in many languages. If some characters can't be displayed on your terminal, they appear as '?' or as hollow boxes (see Undisplayable Characters). Keyboards, even in the countries where these character sets are used, generally don't have keys for all the characters in them. You can insert characters that your keyboard does not support, using C-q (quoted-insert) or C-x 8 <RET> (insert-char). See Inserting Text. Emacs also supports various input methods, typically one for each script or language, which make it easier to type characters in the script. See Input Methods. The prefix key C-x <RET> is used for commands that pertain to multibyte characters, coding systems, and input methods. The command C-x = (what-cursor-position) shows information about the character at point. In addition to the character position, which was described in Position Info, this command displays how the character is encoded. For instance, it displays the following line in the echo area for the character 'c': Char: c (99, #o143, #x63) point=28062 of 36168 (78%) column=53  The four values after 'Char:' describe the character that follows point, first by showing it and then by giving its character code in decimal, octal and hex. For a non-ASCII multibyte character, these are followed by 'file' and the character's representation, in hex, in the buffer's coding system, if that coding system encodes the character safely and with a single byte (see Coding Systems). If the character's encoding is longer than one byte, Emacs shows 'file ...'. As a special case, if the character lies in the range 128 (0200 octal) through 159 (0237 octal), it stands for a "raw" byte that does not correspond to any specific displayable character. Such a "character" lies within the eight-bit-control character set, and is displayed as an escaped octal character code. In this case, C-x = shows 'part of display ...' instead of 'file'. With a prefix argument (C-u C-x =), this command displays a detailed description of the character in a window: • The character set name, and the codes that identify the character within that character set; ASCII characters are identified as belonging to the ascii character set. • The character's syntax and categories. • The character's encodings, both internally in the buffer, and externally if you were to save the file. • What keys to type to input the character in the current input method (if it supports the character). • If you are running Emacs on a graphical display, the font name and glyph code for the character. If you are running Emacs on a text terminal, the code(s) sent to the terminal. • The character's text properties, including any non-default faces used to display the character, and any overlays containing it. Here's an example showing the Latin-1 character A with grave accent, in a buffer whose coding system is utf-8-unix:  position: 1 of 1 (0%), column: 0 character: À (displayed as À) (codepoint 192, #o300, #xc0) preferred charset: unicode (Unicode (ISO10646)) code point in charset: 0xC0 syntax: w which means: word category: .:Base, L:Left-to-right (strong), j:Japanese, l:Latin, v:Viet buffer code: #xC3 #x80 file code: not encodable by coding system undecided-unix display: by this font (glyph code) xft:-unknown-DejaVu Sans Mono-normal-normal- normal-*-13-*-*-*-m-0-iso10646-1 (#x82) Character code properties: customize what to show name: LATIN CAPITAL LETTER A WITH GRAVE old-name: LATIN CAPITAL LETTER A GRAVE general-category: Lu (Letter, Uppercase) decomposition: (65 768) ('A' '')  ## Disabling Multibyte Characters By default, Emacs starts in multibyte mode: it stores the contents of buffers and strings using an internal encoding that represents non-ASCII characters using multi-byte sequences. Multibyte mode allows you to use all the supported languages and scripts without limitations. Under very special circumstances, you may want to disable multibyte character support, for a specific buffer. When multibyte characters are disabled in a buffer, we call that unibyte mode. In unibyte mode, each character in the buffer has a character code ranging from 0 through 255 (0377 octal); 0 through 127 (0177 octal) represent ASCII characters, and 128 (0200 octal) through 255 (0377 octal) represent non-ASCII characters. To edit a particular file in unibyte representation, visit it using find-file-literally. See Visiting. You can convert a multibyte buffer to unibyte by saving it to a file, killing the buffer, and visiting the file again with find-file-literally. Alternatively, you can use C-x <RET> c (universal-coding-system-argument) and specify 'raw-text' as the coding system with which to visit or save a file. See Text Coding. Unlike find-file-literally, finding a file as 'raw-text' doesn't disable format conversion, uncompression, or auto mode selection. Emacs normally loads Lisp files as multibyte. This includes the Emacs initialization file, .emacs, and the initialization files of packages such as Gnus. However, you can specify unibyte loading for a particular Lisp file, by adding an entry 'coding: raw-text' in a file local variables section. See Specify Coding. Then that file is always loaded as unibyte text. You can also load a Lisp file as unibyte, on any one occasion, by typing C-x <RET> c raw-text <RET> immediately before loading it. The buffer-local variable enable-multibyte-characters is non-nil in multibyte buffers, and nil in unibyte ones. The mode line also indicates whether a buffer is multibyte or not. See Mode Line. With a graphical display, in a multibyte buffer, the portion of the mode line that indicates the character set has a tooltip that (amongst other things) says that the buffer is multibyte. In a unibyte buffer, the character set indicator is absent. Thus, in a unibyte buffer (when using a graphical display) there is normally nothing before the indication of the visited file's end-of-line convention (colon, backslash, etc.), unless you are using an input method. You can turn off multibyte support in a specific buffer by invoking the command toggle-enable-multibyte-characters in that buffer. ## Language Environments All supported character sets are supported in Emacs buffers whenever multibyte characters are enabled; there is no need to select a particular language to display its characters. However, it is important to select a language environment to set various defaults. Roughly speaking, the language environment represents a choice of preferred script rather than a choice of language. The language environment controls which coding systems to recognize when reading text (see Recognize Coding). This applies to files, incoming mail, and any other text you read into Emacs. It may also specify the default coding system to use when you create a file. Each language environment also specifies a default input method. To select a language environment, customize current-language-environment or use the command M-x set-language-environment. It makes no difference which buffer is current when you use this command, because the effects apply globally to the Emacs session. The supported language environments (see the variable language-info-alist) include: • ASCII • Belarusian • Bengali • Brazilian Portuguese • Bulgarian • Cham • Chinese-BIG5 • Chinese-CNS • Chinese-EUC-TW • Chinese-GB • Chinese-GBK • Chinese-GB18030 • Croatian • Cyrillic-Alt • Cyrillic-ISO • Cyrillic-KOI8 • Czech • Devanagari • Dutch • English • Esperanto • Ethiopic • French • Georgian • German • Greek • Gujarati • Hebrew • IPA • Italian • Japanese • Kannada • Khmer • Korean • Lao • Latin-1 • Latin-2 • Latin-3 • Latin-4 • Latin-5 • Latin-6 • Latin-7 • Latin-8 (Celtic) • Latin-9 (updated Latin-1 with the Euro sign) • Latvian • Lithuanian • Malayalam • Oriya • Polish • Punjabi • Romanian • Russian • Sinhala • Slovak • Slovenian • Spanish • Swedish • TaiViet • Tajik • Tamil • Telugu • Thai • Tibetan • Turkish • UTF-8 (for a setup which prefers Unicode characters and files encoded in UTF-8) • Ukrainian • Vietnamese • Welsh • Windows-1255 (for a setup which prefers Cyrillic characters and files encoded in Windows-1255). To display the script(s) used by your language environment on a graphical display, you need to have suitable fonts. See Fontsets, for more details about setting up your fonts. Some operating systems let you specify the character-set locale you are using by setting the locale environment variables LC_ALL, LC_CTYPE, or LANG. (If more than one of these is set, the first one that is nonempty specifies your locale for this purpose.) During startup, Emacs looks up your character-set locale's name in the system locale alias table, matches its canonical name against entries in the value of the variables locale-charset-language-names and locale-language-names (the former overrides the latter), and selects the corresponding language environment if a match is found. It also adjusts the display table and terminal coding system, the locale coding system, the preferred coding system as needed for the locale, and—last but not least—the way Emacs decodes non-ASCII characters sent by your keyboard. If you modify the LC_ALL, LC_CTYPE, or LANG environment variables while running Emacs (by using M-x setenv), you may want to invoke the set-locale-environment function afterwards to readjust the language environment from the new locale. The set-locale-environment function normally uses the preferred coding system established by the language environment to decode system messages. But if your locale matches an entry in the variable locale-preferred-coding-systems, Emacs uses the corresponding coding system instead. For example, if the locale 'ja_JP.PCK' matches japanese-shift-jis in locale-preferred-coding-systems, Emacs uses that encoding even though it might normally use japanese-iso-8bit. You can override the language environment chosen at startup with explicit use of the command set-language-environment, or with customization of current-language-environment in your init file. To display information about the effects of a certain language environment lang-env, use the command C-h L lang-env <RET> (describe-language-environment). This tells you which languages this language environment is useful for, and lists the character sets, coding systems, and input methods that go with it. It also shows some sample text to illustrate scripts used in this language environment. If you give an empty input for lang-env, this command describes the chosen language environment. You can customize any language environment with the normal hook set-language-environment-hook. The command set-language-environment runs that hook after setting up the new language environment. The hook functions can test for a specific language environment by checking the variable current-language-environment. This hook is where you should put non-default settings for specific language environments, such as coding systems for keyboard input and terminal output, the default input method, etc. Before it starts to set up the new language environment, set-language-environment first runs the hook exit-language-environment-hook. This hook is useful for undoing customizations that were made with set-language-environment-hook. For instance, if you set up a special key binding in a specific language environment using set-language-environment-hook, you should set up exit-language-environment-hook to restore the normal binding for that key. ## Input Methods An input method is a kind of character conversion designed specifically for interactive input. In Emacs, typically each language has its own input method; sometimes several languages that use the same characters can share one input method. A few languages support several input methods. The simplest kind of input method works by mapping ASCII letters into another alphabet; this allows you to use one other alphabet instead of ASCII. The Greek and Russian input methods work this way. A more powerful technique is composition: converting sequences of characters into one letter. Many European input methods use composition to produce a single non-ASCII letter from a sequence that consists of a letter followed by accent characters (or vice versa). For example, some methods convert the sequence o ^ into a single accented letter. These input methods have no special commands of their own; all they do is compose sequences of printing characters. The input methods for syllabic scripts typically use mapping followed by composition. The input methods for Thai and Korean work this way. First, letters are mapped into symbols for particular sounds or tone marks; then, sequences of these that make up a whole syllable are mapped into one syllable sign. Chinese and Japanese require more complex methods. In Chinese input methods, first you enter the phonetic spelling of a Chinese word (in input method chinese-py, among others), or a sequence of portions of the character (input methods chinese-4corner and chinese-sw, and others). One input sequence typically corresponds to many possible Chinese characters. You select the one you mean using keys such as C-f, C-b, C-n, C-p (or the arrow keys), and digits, which have special meanings in this situation. The possible characters are conceptually arranged in several rows, with each row holding up to 10 alternatives. Normally, Emacs displays just one row at a time, in the echo area; (i/j) appears at the beginning, to indicate that this is the ith row out of a total of j rows. Type C-n or C-p to display the next row or the previous row. Type C-f and C-b to move forward and backward among the alternatives in the current row. As you do this, Emacs highlights the current alternative with a special color; type C-<SPC> to select the current alternative and use it as input. The alternatives in the row are also numbered; the number appears before the alternative. Typing a number selects the associated alternative of the current row and uses it as input. <TAB> in these Chinese input methods displays a buffer showing all the possible characters at once; then clicking Mouse-2 on one of them selects that alternative. The keys C-f, C-b, C-n, C-p, and digits continue to work as usual, but they do the highlighting in the buffer showing the possible characters, rather than in the echo area. In Japanese input methods, first you input a whole word using phonetic spelling; then, after the word is in the buffer, Emacs converts it into one or more characters using a large dictionary. One phonetic spelling corresponds to a number of different Japanese words; to select one of them, use C-n and C-p to cycle through the alternatives. Sometimes it is useful to cut off input method processing so that the characters you have just entered will not combine with subsequent characters. For example, in input method latin-1-postfix, the sequence o ^ combines to form an 'o' with an accent. What if you want to enter them as separate characters? One way is to type the accent twice; this is a special feature for entering the separate letter and accent. For example, o ^ ^ gives you the two characters 'o^'. Another way is to type another letter after the o—something that won't combine with that—and immediately delete it. For example, you could type o o <DEL> ^ to get separate 'o' and '^'. Another method, more general but not quite as easy to type, is to use C-\ C-\ between two characters to stop them from combining. This is the command C-\ (toggle-input-method) used twice. See Select Input Method. C-\ C-\ is especially useful inside an incremental search, because it stops waiting for more characters to combine, and starts searching for what you have already entered. To find out how to input the character after point using the current input method, type C-u C-x =. See Position Info. The variables input-method-highlight-flag and input-method-verbose-flag control how input methods explain what is happening. If input-method-highlight-flag is non-nil, the partial sequence is highlighted in the buffer (for most input methods; some disable this feature). If input-method-verbose-flag is non-nil, the list of possible characters to type next is displayed in the echo area (but not when you are in the minibuffer). Another facility for typing characters not on your keyboard is by using C-x 8 <RET> (insert-char) to insert a single character based on its Unicode name or code-point; see Inserting Text. ## Selecting an Input Method  C-\ Enable or disable use of the selected input method (toggle-input-method). C-x C-\ method Select a new input method for the current buffer (set-input-method). C-h I method , C-h C-\ method Describe the input method method (describe-input-method). By default, it describes the current input method (if any). This description should give you the full details of how to use any particular input method. M-x list-input-methods Display a list of all the supported input methods. To choose an input method for the current buffer, use C-x <RET> C-\ (set-input-method). This command reads the input method name from the minibuffer; the name normally starts with the language environment that it is meant to be used with. The variable current-input-method records which input method is selected. Input methods use various sequences of ASCII characters to stand for non-ASCII characters. Sometimes it is useful to turn off the input method temporarily. To do this, type C-\ (toggle-input-method). To reenable the input method, type C-\ again. If you type C-\ and you have not yet selected an input method, it prompts you to specify one. This has the same effect as using C-x <RET> C-\ to specify an input method. When invoked with a numeric argument, as in C-u C-\, toggle-input-method always prompts you for an input method, suggesting the most recently selected one as the default. Selecting a language environment specifies a default input method for use in various buffers. When you have a default input method, you can select it in the current buffer by typing C-\. The variable default-input-method specifies the default input method (nil means there is none). In some language environments, which support different input methods, you might want to use an input method different from the default chosen by set-language-environment. You can instruct Emacs to select a different default input method for a certain language environment, if you wish, by using set-language-environment-hook (see set-language-environment-hook). For example: (defun my-chinese-setup () "Set up my private Chinese environment." (if (equal current-language-environment "Chinese-GB") (setq default-input-method "chinese-tonepy"))) (add-hook 'set-language-environment-hook 'my-chinese-setup)  This sets the default input method to be chinese-tonepy whenever you choose a Chinese-GB language environment. You can instruct Emacs to activate a certain input method automatically. For example: (add-hook 'text-mode-hook (lambda () (set-input-method "german-prefix")))  This automatically activates the input method "german-prefix" in Text mode. Some input methods for alphabetic scripts work by (in effect) remapping the keyboard to emulate various keyboard layouts commonly used for those scripts. How to do this remapping properly depends on your actual keyboard layout. To specify which layout your keyboard has, use the command M-x quail-set-keyboard-layout. You can use the command M-x quail-show-key to show what key (or key sequence) to type to input the character following point, using the selected keyboard layout. The command C-u C-x = also shows that information, in addition to other information about the character. M-x list-input-methods displays a list of all the supported input methods. The list gives information about each input method, including the string that stands for it in the mode line. ## Coding Systems Users of various languages have established many more-or-less standard coding systems for representing them. Emacs does not use these coding systems internally; instead, it converts from various coding systems to its own system when reading data, and converts the internal coding system to other coding systems when writing data. Conversion is possible in reading or writing files, in sending or receiving from the terminal, and in exchanging data with subprocesses. Emacs assigns a name to each coding system. Most coding systems are used for one language, and the name of the coding system starts with the language name. Some coding systems are used for several languages; their names usually start with 'iso'. There are also special coding systems, such as no-conversion, raw-text, and emacs-internal. A special class of coding systems, collectively known as codepages, is designed to support text encoded by MS Windows and MS-DOS software. The names of these coding systems are cpnnnn, where nnnn is a 3- or 4-digit number of the codepage. You can use these encodings just like any other coding system; for example, to visit a file encoded in codepage 850, type C-x <RET> c cp850 <RET> C-x C-f filename <RET>. In addition to converting various representations of non-ASCII characters, a coding system can perform end-of-line conversion. Emacs handles three different conventions for how to separate lines in a file: newline ("unix"), carriage-return linefeed ("dos"), and just carriage-return ("mac").  C-h C coding Describe coding system coding (describe-coding-system). C-h C Describe the coding systems currently in use. M-x list-coding-systems Display a list of all the supported coding systems. The command C-h C (describe-coding-system) displays information about particular coding systems, including the end-of-line conversion specified by those coding systems. You can specify a coding system name as the argument; alternatively, with an empty argument, it describes the coding systems currently selected for various purposes, both in the current buffer and as the defaults, and the priority list for recognizing coding systems (see Recognize Coding). To display a list of all the supported coding systems, type M-x list-coding-systems. The list gives information about each coding system, including the letter that stands for it in the mode line (see Mode Line). Each of the coding systems that appear in this list—except for no-conversion, which means no conversion of any kind—specifies how and whether to convert printing characters, but leaves the choice of end-of-line conversion to be decided based on the contents of each file. For example, if the file appears to use the sequence carriage-return linefeed to separate lines, DOS end-of-line conversion will be used. Each of the listed coding systems has three variants, which specify exactly what to do for end-of-line conversion:  ...-unix Don't do any end-of-line conversion; assume the file uses newline to separate lines. (This is the convention normally used on Unix and GNU systems, and Mac OS X.) ...-dos Assume the file uses carriage-return linefeed to separate lines, and do the appropriate conversion. (This is the convention normally used on Microsoft systems.) ...-mac Assume the file uses carriage-return to separate lines, and do the appropriate conversion. (This was the convention used on the Macintosh system prior to OS X.) These variant coding systems are omitted from the list-coding-systems display for brevity, since they are entirely predictable. For example, the coding system iso-latin-1 has variants iso-latin-1-unix, iso-latin-1-dos and iso-latin-1-mac. The coding systems unix, dos, and mac are aliases for undecided-unix, undecided-dos, and undecided-mac, respectively. These coding systems specify only the end-of-line conversion, and leave the character code conversion to be deduced from the text itself. The coding system raw-text is good for a file which is mainly ASCII text, but may contain byte values above 127 that are not meant to encode non-ASCII characters. With raw-text, Emacs copies those byte values unchanged, and sets enable-multibyte-characters to nil in the current buffer so that they will be interpreted properly. raw-text handles end-of-line conversion in the usual way, based on the data encountered, and has the usual three variants to specify the kind of end-of-line conversion to use. In contrast, the coding system no-conversion specifies no character code conversion at all—none for non-ASCII byte values and none for end of line. This is useful for reading or writing binary files, tar files, and other files that must be examined verbatim. It, too, sets enable-multibyte-characters to nil. The easiest way to edit a file with no conversion of any kind is with the M-x find-file-literally command. This uses no-conversion, and also suppresses other Emacs features that might convert the file contents before you see them. See Visiting. The coding system emacs-internal (or utf-8-emacs, which is equivalent) means that the file contains non-ASCII characters stored with the internal Emacs encoding. This coding system handles end-of-line conversion based on the data encountered, and has the usual three variants to specify the kind of end-of-line conversion. ## Recognizing Coding Systems Whenever Emacs reads a given piece of text, it tries to recognize which coding system to use. This applies to files being read, output from subprocesses, text from X selections, etc. Emacs can select the right coding system automatically most of the time—once you have specified your preferences. Some coding systems can be recognized or distinguished by which byte sequences appear in the data. However, there are coding systems that cannot be distinguished, not even potentially. For example, there is no way to distinguish between Latin-1 and Latin-2; they use the same byte values with different meanings. Emacs handles this situation by means of a priority list of coding systems. Whenever Emacs reads a file, if you do not specify the coding system to use, Emacs checks the data against each coding system, starting with the first in priority and working down the list, until it finds a coding system that fits the data. Then it converts the file contents assuming that they are represented in this coding system. The priority list of coding systems depends on the selected language environment (see Language Environments). For example, if you use French, you probably want Emacs to prefer Latin-1 to Latin-2; if you use Czech, you probably want Latin-2 to be preferred. This is one of the reasons to specify a language environment. However, you can alter the coding system priority list in detail with the command M-x prefer-coding-system. This command reads the name of a coding system from the minibuffer, and adds it to the front of the priority list, so that it is preferred to all others. If you use this command several times, each use adds one element to the front of the priority list. If you use a coding system that specifies the end-of-line conversion type, such as iso-8859-1-dos, what this means is that Emacs should attempt to recognize iso-8859-1 with priority, and should use DOS end-of-line conversion when it does recognize iso-8859-1. Sometimes a file name indicates which coding system to use for the file. The variable file-coding-system-alist specifies this correspondence. There is a special function modify-coding-system-alist for adding elements to this list. For example, to read and write all '.txt' files using the coding system chinese-iso-8bit, you can execute this Lisp expression: (modify-coding-system-alist 'file "\\.txt\\'" 'chinese-iso-8bit) The first argument should be file, the second argument should be a regular expression that determines which files this applies to, and the third argument says which coding system to use for these files. Emacs recognizes which kind of end-of-line conversion to use based on the contents of the file: if it sees only carriage-returns, or only carriage-return linefeed sequences, then it chooses the end-of-line conversion accordingly. You can inhibit the automatic use of end-of-line conversion by setting the variable inhibit-eol-conversion to non-nil. If you do that, DOS-style files will be displayed with the '^M' characters visible in the buffer; some people prefer this to the more subtle '(DOS)' end-of-line type indication near the left edge of the mode line (see eol-mnemonic). By default, the automatic detection of coding system is sensitive to escape sequences. If Emacs sees a sequence of characters that begin with an escape character, and the sequence is valid as an ISO-2022 code, that tells Emacs to use one of the ISO-2022 encodings to decode the file. However, there may be cases that you want to read escape sequences in a file as is. In such a case, you can set the variable inhibit-iso-escape-detection to non-nil. Then the code detection ignores any escape sequences, and never uses an ISO-2022 encoding. The result is that all escape sequences become visible in the buffer. The default value of inhibit-iso-escape-detection is nil. We recommend that you not change it permanently, only for one specific operation. That's because some Emacs Lisp source files in the Emacs distribution contain non-ASCII characters encoded in the coding system iso-2022-7bit, and they won't be decoded correctly when you visit those files if you suppress the escape sequence detection. The variables auto-coding-alist and auto-coding-regexp-alist are the strongest way to specify the coding system for certain patterns of file names, or for files containing certain patterns, respectively. These variables even override '-*-coding:-*-' tags in the file itself (see Specify Coding). For example, Emacs uses auto-coding-alist for tar and archive files, to prevent it from being confused by a '-*-coding:-*-' tag in a member of the archive and thinking it applies to the archive file as a whole. Another way to specify a coding system is with the variable auto-coding-functions. For example, one of the builtin auto-coding-functions detects the encoding for XML files. Unlike the previous two, this variable does not override any '-*-coding:-*-' tag. When you get new mail in Rmail, each message is translated automatically from the coding system it is written in, as if it were a separate file. This uses the priority list of coding systems that you have specified. If a MIME message specifies a character set, Rmail obeys that specification. For reading and saving Rmail files themselves, Emacs uses the coding system specified by the variable rmail-file-coding-system. The default value is nil, which means that Rmail files are not translated (they are read and written in the Emacs internal character code). ## Specifying a File's Coding System If Emacs recognizes the encoding of a file incorrectly, you can reread the file using the correct coding system with C-x <RET> r (revert-buffer-with-coding-system). This command prompts for the coding system to use. To see what coding system Emacs actually used to decode the file, look at the coding system mnemonic letter near the left edge of the mode line (see Mode Line), or type C-h C (describe-coding-system). You can specify the coding system for a particular file in the file itself, using the '-*-...-*-' construct at the beginning, or a local variables list at the end (see File Variables). You do this by defining a value for the "variable" named coding. Emacs does not really have a variable coding; instead of setting a variable, this uses the specified coding system for the file. For example, '-*-mode: C; coding: latin-1;-*-' specifies use of the Latin-1 coding system, as well as C mode. When you specify the coding explicitly in the file, that overrides file-coding-system-alist. ## Choosing Coding Systems for Output Once Emacs has chosen a coding system for a buffer, it stores that coding system in buffer-file-coding-system. That makes it the default for operations that write from this buffer into a file, such as save-buffer and write-region. You can specify a different coding system for further file output from the buffer using set-buffer-file-coding-system (see Text Coding). You can insert any character Emacs supports into any Emacs buffer, but most coding systems can only handle a subset of these characters. Therefore, it's possible that the characters you insert cannot be encoded with the coding system that will be used to save the buffer. For example, you could visit a text file in Polish, encoded in iso-8859-2, and add some Russian words to it. When you save that buffer, Emacs cannot use the current value of buffer-file-coding-system, because the characters you added cannot be encoded by that coding system. When that happens, Emacs tries the most-preferred coding system (set by M-x prefer-coding-system or M-x set-language-environment). If that coding system can safely encode all of the characters in the buffer, Emacs uses it, and stores its value in buffer-file-coding-system. Otherwise, Emacs displays a list of coding systems suitable for encoding the buffer's contents, and asks you to choose one of those coding systems. If you insert the unsuitable characters in a mail message, Emacs behaves a bit differently. It additionally checks whether the most-preferred coding system is recommended for use in MIME messages; if not, it informs you of this fact and prompts you for another coding system. This is so you won't inadvertently send a message encoded in a way that your recipient's mail software will have difficulty decoding. (You can still use an unsuitable coding system if you enter its name at the prompt.) When you send a mail message (see Sending Mail), Emacs has four different ways to determine the coding system to use for encoding the message text. It tries the buffer's own value of buffer-file-coding-system, if that is non-nil. Otherwise, it uses the value of sendmail-coding-system, if that is non-nil. The third way is to use the default coding system for new files, which is controlled by your choice of language environment, if that is non-nil. If all of these three values are nil, Emacs encodes outgoing mail using the Latin-1 coding system. ## Specifying a Coding System for File Text In cases where Emacs does not automatically choose the right coding system for a file's contents, you can use these commands to specify one:  C-x f coding Use coding system coding to save or revisit the file in the current buffer (set-buffer-file-coding-system). C-x c coding Specify coding system coding for the immediately following command (universal-coding-system-argument). C-x r coding Revisit the current file using the coding system coding (revert-buffer-with-coding-system). M-x recode-region right wrong Convert a region that was decoded using coding system wrong, decoding it using coding system right instead. The command C-x <RET> f (set-buffer-file-coding-system) sets the file coding system for the current buffer (i.e., the coding system to use when saving or reverting the file). You specify which coding system using the minibuffer. You can also invoke this command by clicking with Mouse-3 on the coding system indicator in the mode line (see Mode Line). If you specify a coding system that cannot handle all the characters in the buffer, Emacs will warn you about the troublesome characters, and ask you to choose another coding system, when you try to save the buffer (see Output Coding). You can also use this command to specify the end-of-line conversion (see end-of-line conversion) for encoding the current buffer. For example, C-x <RET> f dos <RET> will cause Emacs to save the current buffer's text with DOS-style carriage-return linefeed line endings. Another way to specify the coding system for a file is when you visit the file. First use the command C-x <RET> c (universal-coding-system-argument); this command uses the minibuffer to read a coding system name. After you exit the minibuffer, the specified coding system is used for the immediately following command. So if the immediately following command is C-x C-f, for example, it reads the file using that coding system (and records the coding system for when you later save the file). Or if the immediately following command is C-x C-w, it writes the file using that coding system. When you specify the coding system for saving in this way, instead of with C-x <RET> f, there is no warning if the buffer contains characters that the coding system cannot handle. Other file commands affected by a specified coding system include C-x i and C-x C-v, as well as the other-window variants of C-x C-f. C-x <RET> c also affects commands that start subprocesses, including M-x shell (see Shell). If the immediately following command does not use the coding system, then C-x <RET> c ultimately has no effect. An easy way to visit a file with no conversion is with the M-x find-file-literally command. See Visiting. The default value of the variable buffer-file-coding-system specifies the choice of coding system to use when you create a new file. It applies when you find a new file, and when you create a buffer and then save it in a file. Selecting a language environment typically sets this variable to a good choice of default coding system for that language environment. If you visit a file with a wrong coding system, you can correct this with C-x <RET> r (revert-buffer-with-coding-system). This visits the current file again, using a coding system you specify. If a piece of text has already been inserted into a buffer using the wrong coding system, you can redo the decoding of it using M-x recode-region. This prompts you for the proper coding system, then for the wrong coding system that was actually used, and does the conversion. It first encodes the region using the wrong coding system, then decodes it again using the proper coding system. ## Coding Systems for Interprocess Communication This section explains how to specify coding systems for use in communication with other processes.  C-x x coding Use coding system coding for transferring selections to and from other graphical applications (set-selection-coding-system). C-x X coding Use coding system coding for transferring one selection—the next one—to or from another graphical application (set-next-selection-coding-system). C-x p input-coding output-coding Use coding systems input-coding and output-coding for subprocess input and output in the current buffer (set-buffer-process-coding-system). The command C-x <RET> x (set-selection-coding-system) specifies the coding system for sending selected text to other windowing applications, and for receiving the text of selections made in other applications. This command applies to all subsequent selections, until you override it by using the command again. The command C-x <RET> X (set-next-selection-coding-system) specifies the coding system for the next selection made in Emacs or read by Emacs. The variable x-select-request-type specifies the data type to request from the X Window System for receiving text selections from other applications. If the value is nil (the default), Emacs tries UTF8_STRING and COMPOUND_TEXT, in this order, and uses various heuristics to choose the more appropriate of the two results; if none of these succeed, Emacs falls back on STRING. If the value of x-select-request-type is one of the symbols COMPOUND_TEXT, UTF8_STRING, STRING, or TEXT, Emacs uses only that request type. If the value is a list of some of these symbols, Emacs tries only the request types in the list, in order, until one of them succeeds, or until the list is exhausted. The command C-x <RET> p (set-buffer-process-coding-system) specifies the coding system for input and output to a subprocess. This command applies to the current buffer; normally, each subprocess has its own buffer, and thus you can use this command to specify translation to and from a particular subprocess by giving the command in the corresponding buffer. You can also use C-x <RET> c (universal-coding-system-argument) just before the command that runs or starts a subprocess, to specify the coding system for communicating with that subprocess. See Text Coding. The default for translation of process input and output depends on the current language environment. The variable locale-coding-system specifies a coding system to use when encoding and decoding system strings such as system error messages and format-time-string formats and time stamps. That coding system is also used for decoding non-ASCII keyboard input on the X Window System. You should choose a coding system that is compatible with the underlying system's text representation, which is normally specified by one of the environment variables LC_ALL, LC_CTYPE, and LANG. (The first one, in the order specified above, whose value is nonempty is the one that determines the text representation.) ## Coding Systems for File Names  C-x F coding Use coding system coding for encoding and decoding file names (set-file-name-coding-system). The command C-x <RET> F (set-file-name-coding-system) specifies a coding system to use for encoding file names. It has no effect on reading and writing the contents of files. In fact, all this command does is set the value of the variable file-name-coding-system. If you set the variable to a coding system name (as a Lisp symbol or a string), Emacs encodes file names using that coding system for all file operations. This makes it possible to use non-ASCII characters in file names—or, at least, those non-ASCII characters that the specified coding system can encode. If file-name-coding-system is nil, Emacs uses a default coding system determined by the selected language environment, and stored in the default-file-name-coding-system variable. In the default language environment, non-ASCII characters in file names are not encoded specially; they appear in the file system using the internal Emacs representation. Warning: if you change file-name-coding-system (or the language environment) in the middle of an Emacs session, problems can result if you have already visited files whose names were encoded using the earlier coding system and cannot be encoded (or are encoded differently) under the new coding system. If you try to save one of these buffers under the visited file name, saving may use the wrong file name, or it may encounter an error. If such a problem happens, use C-x C-w to specify a new file name for that buffer. If a mistake occurs when encoding a file name, use the command M-x recode-file-name to change the file name's coding system. This prompts for an existing file name, its old coding system, and the coding system to which you wish to convert. ## Coding Systems for Terminal I/O  C-x t coding Use coding system coding for terminal output (set-terminal-coding-system). C-x k coding Use coding system coding for keyboard input (set-keyboard-coding-system). The command C-x <RET> t (set-terminal-coding-system) specifies the coding system for terminal output. If you specify a character code for terminal output, all characters output to the terminal are translated into that coding system. This feature is useful for certain character-only terminals built to support specific languages or character sets—for example, European terminals that support one of the ISO Latin character sets. You need to specify the terminal coding system when using multibyte text, so that Emacs knows which characters the terminal can actually handle. By default, output to the terminal is not translated at all, unless Emacs can deduce the proper coding system from your terminal type or your locale specification (see Language Environments). The command C-x <RET> k (set-keyboard-coding-system), or the variable keyboard-coding-system, specifies the coding system for keyboard input. Character-code translation of keyboard input is useful for terminals with keys that send non-ASCII graphic characters—for example, some terminals designed for ISO Latin-1 or subsets of it. By default, keyboard input is translated based on your system locale setting. If your terminal does not really support the encoding implied by your locale (for example, if you find it inserts a non-ASCII character if you type M-i), you will need to set keyboard-coding-system to nil to turn off encoding. You can do this by putting (set-keyboard-coding-system nil)  in your init file. There is a similarity between using a coding system translation for keyboard input, and using an input method: both define sequences of keyboard input that translate into single characters. However, input methods are designed to be convenient for interactive use by humans, and the sequences that are translated are typically sequences of ASCII printing characters. Coding systems typically translate sequences of non-graphic characters. ## Fontsets A font typically defines shapes for a single alphabet or script. Therefore, displaying the entire range of scripts that Emacs supports requires a collection of many fonts. In Emacs, such a collection is called a fontset. A fontset is defined by a list of font specifications, each assigned to handle a range of character codes, and may fall back on another fontset for characters that are not covered by the fonts it specifies. Each fontset has a name, like a font. However, while fonts are stored in the system and the available font names are defined by the system, fontsets are defined within Emacs itself. Once you have defined a fontset, you can use it within Emacs by specifying its name, anywhere that you could use a single font. Of course, Emacs fontsets can use only the fonts that the system supports. If some characters appear on the screen as empty boxes or hex codes, this means that the fontset in use for them has no font for those characters. In this case, or if the characters are shown, but not as well as you would like, you may need to install extra fonts. Your operating system may have optional fonts that you can install; or you can install the GNU Intlfonts package, which includes fonts for most supported scripts. Emacs creates three fontsets automatically: the standard fontset, the startup fontset and the default fontset. The default fontset is most likely to have fonts for a wide variety of non-ASCII characters, and is the default fallback for the other two fontsets, and if you set a default font rather than fontset. However, it does not specify font family names, so results can be somewhat random if you use it directly. You can specify use of a particular fontset by starting Emacs with the '-fn' option. For example, emacs -fn fontset-standard  You can also specify a fontset with the 'Font' resource (see X Resources). If no fontset is specified for use, then Emacs uses an ASCII font, with 'fontset-default' as a fallback for characters the font does not cover. The standard fontset is only used if explicitly requested, despite its name. A fontset does not necessarily specify a font for every character code. If a fontset specifies no font for a certain character, or if it specifies a font that does not exist on your system, then it cannot display that character properly. It will display that character as a hex code or thin space or an empty box instead. (See glyphless characters, for details.) ## Defining Fontsets When running on X, Emacs creates a standard fontset automatically according to the value of standard-fontset-spec. This fontset's name is -*-fixed-medium-r-normal-*-16-*-*-*-*-*-fontset-standard  or just 'fontset-standard' for short. On GNUstep and Mac OS X, the standard fontset is created using the value of ns-standard-fontset-spec, and on MS Windows it is created using the value of w32-standard-fontset-spec. Bold, italic, and bold-italic variants of the standard fontset are created automatically. Their names have 'bold' instead of 'medium', or 'i' instead of 'r', or both. Emacs generates a fontset automatically, based on any default ASCII font that you specify with the 'Font' resource or the '-fn' argument, or the default font that Emacs found when it started. This is the startup fontset and its name is fontset-startup. It does this by replacing the charset_registry field with 'fontset', and replacing charset_encoding field with 'startup', then using the resulting string to specify a fontset. For instance, if you start Emacs with a font of this form, emacs -fn "*courier-medium-r-normal--14-140-*-iso8859-1"  Emacs generates the following fontset and uses it for the initial X window frame: -*-courier-medium-r-normal-*-14-140-*-*-*-*-fontset-startup  The startup fontset will use the font that you specify, or a variant with a different Registry and encoding, for all the characters that are supported by that font, and fallback on 'fontset-default' for other characters. With the X resource 'Emacs.Font', you can specify a fontset name just like an actual font name. But be careful not to specify a fontset name in a wildcard resource like 'Emacs*Font'—that wildcard specification matches other resources, such as for menus, and menus cannot handle fontsets. See X Resources. You can specify additional fontsets using X resources named 'Fontset-n', where n is an integer starting from 0. The resource value should have this form: fontpattern, [charset:font]...  fontpattern should have the form of a standard X font name (see the previous fontset-startup example), except for the last two fields. They should have the form 'fontset-alias'. The fontset has two names, one long and one short. The long name is fontpattern. The short name is 'fontset-alias'. You can refer to the fontset by either name. The construct 'charset:font' specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in defining one fontset. For the other character sets, Emacs chooses a font based on fontpattern. It replaces 'fontset-alias' with values that describe the character set. For the ASCII character font, 'fontset-alias' is replaced with 'ISO8859-1'. Also, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not also useful, because it is better to use the smaller font in its own size, which is what Emacs does. Thus if fontpattern is this, -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24  the font specification for ASCII characters would be this: -*-fixed-medium-r-normal-*-24-*-ISO8859-1  and the font specification for Chinese GB2312 characters would be this: -*-fixed-medium-r-normal-*-24-*-gb2312*-*  You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have 'song ti' or 'fangsong ti' in the family field. In such a case, 'Fontset-n' can be specified as: Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\ chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*  Then, the font specifications for all but Chinese GB2312 characters have 'fixed' in the family field, and the font specification for Chinese GB2312 characters has a wild card '*' in the family field. The function that processes the fontset resource value to create the fontset is called create-fontset-from-fontset-spec. You can also call this function explicitly to create a fontset. See Fonts, for more information about font naming. ## Modifying Fontsets Fontsets do not always have to be created from scratch. If only minor changes are required it may be easier to modify an existing fontset. Modifying 'fontset-default' will also affect other fontsets that use it as a fallback, so can be an effective way of fixing problems with the fonts that Emacs chooses for a particular script. Fontsets can be modified using the function set-fontset-font, specifying a character, a charset, a script, or a range of characters to modify the font for, and a font specification for the font to be used. Some examples are: ;; Use Liberation Mono for latin-3 charset. (set-fontset-font "fontset-default" 'iso-8859-3 "Liberation Mono") ;; Prefer a big5 font for han characters (set-fontset-font "fontset-default" 'han (font-spec :registry "big5") nil 'prepend) ;; Use DejaVu Sans Mono as a fallback in fontset-startup ;; before resorting to fontset-default. (set-fontset-font "fontset-startup" nil "DejaVu Sans Mono" nil 'append) ;; Use MyPrivateFont for the Unicode private use area. (set-fontset-font "fontset-default" '(#xe000 . #xf8ff) "MyPrivateFont") ## Undisplayable Characters There may be some non-ASCII characters that your terminal cannot display. Most text terminals support just a single character set (use the variable default-terminal-coding-system to tell Emacs which one; see Terminal Coding); characters that can't be encoded in that coding system are displayed as '?' by default. Graphical displays can display a broader range of characters, but you may not have fonts installed for all of them; characters that have no font appear as a hollow box. If you use Latin-1 characters but your terminal can't display Latin-1, you can arrange to display mnemonic ASCII sequences instead, e.g., '"o' for o-umlaut. Load the library iso-ascii to do this. If your terminal can display Latin-1, you can display characters from other European character sets using a mixture of equivalent Latin-1 characters and ASCII mnemonics. Customize the variable latin1-display to enable this. The mnemonic ASCII sequences mostly correspond to those of the prefix input methods. ## Unibyte Editing Mode The ISO 8859 Latin-n character sets define character codes in the range 0240 to 0377 octal (160 to 255 decimal) to handle the accented letters and punctuation needed by various European languages (and some non-European ones). Note that Emacs considers bytes with codes in this range as raw bytes, not as characters, even in a unibyte buffer, i.e., if you disable multibyte characters. However, Emacs can still handle these character codes as if they belonged to one of the single-byte character sets at a time. To specify which of these codes to use, invoke M-x set-language-environment and specify a suitable language environment such as 'Latin-n'. For more information about unibyte operation, see Disabling Multibyte. Emacs can also display bytes in the range 160 to 255 as readable characters, provided the terminal or font in use supports them. This works automatically. On a graphical display, Emacs can also display single-byte characters through fontsets, in effect by displaying the equivalent multibyte characters according to the current language environment. To request this, set the variable unibyte-display-via-language-environment to a non-nil value. Note that setting this only affects how these bytes are displayed, but does not change the fundamental fact that Emacs treats them as raw bytes, not as characters. If your terminal does not support display of the Latin-1 character set, Emacs can display these characters as ASCII sequences which at least give you a clear idea of what the characters are. To do this, load the library iso-ascii. Similar libraries for other Latin-n character sets could be implemented, but have not been so far. Normally non-ISO-8859 characters (decimal codes between 128 and 159 inclusive) are displayed as octal escapes. You can change this for non-standard "extended" versions of ISO-8859 character sets by using the function standard-display-8bit in the disp-table library. There are two ways to input single-byte non-ASCII characters: • You can use an input method for the selected language environment. See Input Methods. When you use an input method in a unibyte buffer, the non-ASCII character you specify with it is converted to unibyte. • If your keyboard can generate character codes 128 (decimal) and up, representing non-ASCII characters, you can type those character codes directly. On a graphical display, you should not need to do anything special to use these keys; they should work. On a text terminal, you should use the command M-x set-keyboard-coding-system or customize the variable keyboard-coding-system to specify which coding system your keyboard uses (see Terminal Coding). Enabling this feature will probably require you to use <ESC> to type Meta characters; however, on a console terminal or in xterm, you can arrange for Meta to be converted to <ESC> and still be able type 8-bit characters present directly on the keyboard or using Compose or AltGr keys. See User Input. • For Latin-1 only, you can use the key C-x 8 as a "compose character" prefix for entry of non-ASCII Latin-1 printing characters. C-x 8 is good for insertion (in the minibuffer as well as other buffers), for searching, and in any other context where a key sequence is allowed. C-x 8 works by loading the iso-transl library. Once that library is loaded, the <Alt> modifier key, if the keyboard has one, serves the same purpose as C-x 8: use <Alt> together with an accent character to modify the following letter. Also, if the keyboard has keys for the Latin-1 "dead accent characters", they too are defined to compose with the following character, once iso-transl is loaded. Use C-x 8 C-h to list all the available C-x 8 translations. ## Charsets In Emacs, charset is short for "character set". Emacs supports most popular charsets (such as ascii, iso-8859-1, cp1250, big5, and unicode), in addition to some charsets of its own (such as emacs, unicode-bmp, and eight-bit). All supported characters belong to one or more charsets. Emacs normally "does the right thing" with respect to charsets, so that you don't have to worry about them. However, it is sometimes helpful to know some of the underlying details about charsets. One example is font selection (see Fonts). Each language environment (see Language Environments) defines a "priority list" for the various charsets. When searching for a font, Emacs initially attempts to find one that can display the highest-priority charsets. For instance, in the Japanese language environment, the charset japanese-jisx0208 has the highest priority, so Emacs tries to use a font whose Registry property is 'JISX0208.1983-0'. There are two commands that can be used to obtain information about charsets. The command M-x list-charset-chars prompts for a charset name, and displays all the characters in that character set. The command M-x describe-character-set prompts for a charset name, and displays information about that charset, including its internal representation within Emacs. M-x list-character-sets displays a list of all supported charsets. The list gives the names of charsets and additional information to identity each charset; see the International Register of Coded Character Sets for more details. In this list, charsets are divided into two categories: normal charsets are listed first, followed by supplementary charsets. A supplementary charset is one that is used to define another charset (as a parent or a subset), or to provide backward-compatibility for older Emacs versions. To find out which charset a character in the buffer belongs to, put point before it and type C-u C-x = (see International Chars). ## Bidirectional Editing Emacs supports editing text written in scripts, such as Arabic and Hebrew, whose natural ordering of horizontal text for display is from right to left. However, digits and Latin text embedded in these scripts are still displayed left to right. It is also not uncommon to have small portions of text in Arabic or Hebrew embedded in an otherwise Latin document; e.g., as comments and strings in a program source file. For these reasons, text that uses these scripts is actually bidirectional: a mixture of runs of left-to-right and right-to-left characters. This section describes the facilities and options provided by Emacs for editing bidirectional text. Emacs stores right-to-left and bidirectional text in the so-called logical (or reading) order: the buffer or string position of the first character you read precedes that of the next character. Reordering of bidirectional text into the visual order happens at display time. As result, character positions no longer increase monotonically with their positions on display. Emacs implements the Unicode Bidirectional Algorithm described in the Unicode Standard Annex #9, for reordering of bidirectional text for display. The buffer-local variable bidi-display-reordering controls whether text in the buffer is reordered for display. If its value is non-nil, Emacs reorders characters that have right-to-left directionality when they are displayed. The default value is t. Each paragraph of bidirectional text can have its own base direction, either right-to-left or left-to-right. (Paragraph boundaries are empty lines, i.e., lines consisting entirely of whitespace characters.) Text in left-to-right paragraphs begins on the screen at the left margin of the window and is truncated or continued when it reaches the right margin. By contrast, text in right-to-left paragraphs is displayed starting at the right margin and is continued or truncated at the left margin. Emacs determines the base direction of each paragraph dynamically, based on the text at the beginning of the paragraph. However, sometimes a buffer may need to force a certain base direction for its paragraphs. The variable bidi-paragraph-direction, if non-nil, disables the dynamic determination of the base direction, and instead forces all paragraphs in the buffer to have the direction specified by its buffer-local value. The value can be either right-to-left or left-to-right. Any other value is interpreted as nil. Alternatively, you can control the base direction of a paragraph by inserting special formatting characters in front of the paragraph. The special character RIGHT-TO-LEFT MARK, or rlm, forces the right-to-left direction on the following paragraph, while LEFT-TO-RIGHT MARK, or lrm forces the left-to-right direction. (You can use C-x 8 <RET> to insert these characters.) In a GUI session, the lrm and rlm characters display as very thin blank characters; on text terminals they display as blanks. Because characters are reordered for display, Emacs commands that operate in the logical order or on stretches of buffer positions may produce unusual effects. For example, C-f and C-b commands move point in the logical order, so the cursor will sometimes jump when point traverses reordered bidirectional text. Similarly, a highlighted region covering a contiguous range of character positions may look discontinuous if the region spans reordered text. This is normal and similar to the behavior of other programs that support bidirectional text. ## Modes, Major and Minor Emacs contains many editing modes that alter its basic behavior in useful ways. These are divided into major modes and minor modes. Major modes provide specialized facilities for working on a particular file type, such as a C source file (see Programs), or a particular type of non-file buffer, such as a shell buffer (see Shell). Major modes are mutually exclusive; each buffer has one and only one major mode at any time. Minor modes are optional features which you can turn on or off, not necessarily specific to a type of file or buffer. For example, Auto Fill mode is a minor mode in which <SPC> breaks lines between words as you type (see Auto Fill). Minor modes are independent of one another, and of the selected major mode. • Major Modes: Text mode vs. Lisp mode vs. C mode... • Minor Modes: Each minor mode is a feature you can turn on independently of any others. • Choosing Modes: How modes are chosen when visiting files. ## Major Modes Every buffer possesses a major mode, which determines the editing behavior of Emacs while that buffer is current. The mode line normally shows the name of the current major mode, in parentheses (see Mode Line). The least specialized major mode is called Fundamental mode. This mode has no mode-specific redefinitions or variable settings, so that each Emacs command behaves in its most general manner, and each user option variable is in its default state. For editing text of a specific type that Emacs knows about, such as Lisp code or English text, you typically use a more specialized major mode, such as Lisp mode or Text mode. Most major modes fall into three major groups. The first group contains modes for normal text, either plain or with mark-up. It includes Text mode, HTML mode, SGML mode, TeX mode and Outline mode. The second group contains modes for specific programming languages. These include Lisp mode (which has several variants), C mode, Fortran mode, and others. The third group consists of major modes that are not associated directly with files; they are used in buffers created for specific purposes by Emacs, such as Dired mode for buffers made by Dired (see Dired), Message mode for buffers made by C-x m (see Sending Mail), and Shell mode for buffers used to communicate with an inferior shell process (see Interactive Shell). Usually, the major mode is automatically set by Emacs, when you first visit a file or create a buffer (see Choosing Modes). You can explicitly select a new major mode by using an M-x command. Take the name of the mode and add -mode to get the name of the command to select that mode (e.g., M-x lisp-mode enters Lisp mode). The value of the buffer-local variable major-mode is a symbol with the same name as the major mode command (e.g., lisp-mode). This variable is set automatically; you should not change it yourself. The default value of major-mode determines the major mode to use for files that do not specify a major mode, and for new buffers created with C-x b. Normally, this default value is the symbol fundamental-mode, which specifies Fundamental mode. You can change this default value via the Customization interface (see Easy Customization), or by adding a line like this to your init file (see Init File): (setq-default major-mode 'text-mode)  If the default value of major-mode is nil, the major mode is taken from the previously current buffer. Specialized major modes often change the meanings of certain keys to do something more suitable for the mode. For instance, programming language modes bind <TAB> to indent the current line according to the rules of the language (see Indentation). The keys that are commonly changed are <TAB>, <DEL>, and C-j. Many modes also define special commands of their own, usually bound in the prefix key C-c. Major modes can also alter user options and variables; for instance, programming language modes typically set a buffer-local value for the variable comment-start, which determines how source code comments are delimited (see Comments). To view the documentation for the current major mode, including a list of its key bindings, type C-h m (describe-mode). Every major mode, apart from Fundamental mode, defines a mode hook, a customizable list of Lisp functions to run each time the mode is enabled in a buffer. See Hooks, for more information about hooks. Each mode hook is named after its major mode, e.g., Fortran mode has fortran-mode-hook. Furthermore, all text-based major modes run text-mode-hook, and all programming language modes run prog-mode-hook, prior to running their own mode hooks. Hook functions can look at the value of the variable major-mode to see which mode is actually being entered. Mode hooks are commonly used to enable minor modes (see Minor Modes). For example, you can put the following lines in your init file to enable Flyspell minor mode in all text-based major modes (see Spelling), and Eldoc minor mode in Emacs Lisp mode (see Lisp Doc): (add-hook 'text-mode-hook 'flyspell-mode) (add-hook 'emacs-lisp-mode-hook 'eldoc-mode)  ## Minor Modes A minor mode is an optional editing mode that alters the behavior of Emacs in some well-defined way. Unlike major modes, any number of minor modes can be in effect at any time. Some minor modes are buffer-local, and can be turned on (enabled) in certain buffers and off (disabled) in others. Other minor modes are global: while enabled, they affect everything you do in the Emacs session, in all buffers. Most minor modes are disabled by default, but a few are enabled by default. Most buffer-local minor modes say in the mode line when they are enabled, just after the major mode indicator. For example, 'Fill' in the mode line means that Auto Fill mode is enabled. See Mode Line. Like major modes, each minor mode is associated with a mode command, whose name consists of the mode name followed by '-mode'. For instance, the mode command for Auto Fill mode is auto-fill-mode. But unlike a major mode command, which enables the mode, the mode command for a minor mode can either enable or disable it: • If you invoke the mode command directly with no prefix argument (either via M-x, or by binding it to a key and typing that key; see Key Bindings), that toggles the minor mode. The minor mode is turned on if it was off, and turned off if it was on. • If you invoke the mode command with a prefix argument, the minor mode is unconditionally turned off if that argument is zero or negative; otherwise, it is unconditionally turned on. • If the mode command is called via Lisp, the minor mode is unconditionally turned on if the argument is omitted or nil. This makes it easy to turn on a minor mode from a major mode's mode hook (see Major Modes). A non-nil argument is handled like an interactive prefix argument, as described above. Most minor modes also have a mode variable, with the same name as the mode command. Its value is non-nil if the mode is enabled, and nil if it is disabled. In general, you should not try to enable or disable the mode by changing the value of the mode variable directly in Lisp; you should run the mode command instead. However, setting the mode variable through the Customize interface (see Easy Customization) will always properly enable or disable the mode, since Customize automatically runs the mode command for you. The following is a list of some buffer-local minor modes: • Abbrev mode automatically expands text based on pre-defined abbreviation definitions. See Abbrevs. • Auto Fill mode inserts newlines as you type to prevent lines from becoming too long. See Filling. • Auto Save mode saves the buffer contents periodically to reduce the amount of work you can lose in case of a crash. See Auto Save. • Enriched mode enables editing and saving of formatted text. See Enriched Text. • Flyspell mode automatically highlights misspelled words. See Spelling. • Font-Lock mode automatically highlights certain textual units found in programs. It is enabled globally by default, but you can disable it in individual buffers. See Faces. • Linum mode displays each line's line number in the window's left margin. • Outline minor mode provides similar facilities to the major mode called Outline mode. See Outline Mode. • Overwrite mode causes ordinary printing characters to replace existing text instead of shoving it to the right. For example, if point is in front of the 'B' in 'FOOBAR', then in Overwrite mode typing a G changes it to 'FOOGAR', instead of producing 'FOOGBAR' as usual. In Overwrite mode, the command C-q inserts the next character whatever it may be, even if it is a digit—this gives you a way to insert a character instead of replacing an existing character. The mode command, overwrite-mode, is bound to the <Insert> key. • Binary Overwrite mode is a variant of Overwrite mode for editing binary files; it treats newlines and tabs like other characters, so that they overwrite other characters and can be overwritten by them. In Binary Overwrite mode, digits after C-q specify an octal character code, as usual. • Visual Line mode performs "word wrapping", causing long lines to be wrapped at word boundaries. See Visual Line Mode. And here are some useful global minor modes: • Column Number mode enables display of the current column number in the mode line. See Mode Line. • Delete Selection mode causes text insertion to first delete the text in the region, if the region is active. See Using Region. • Icomplete mode displays an indication of available completions when you are in the minibuffer and completion is active. See Options. • Line Number mode enables display of the current line number in the mode line. It is enabled by default. See Mode Line. • Menu Bar mode gives each frame a menu bar. It is enabled by default. See Menu Bars. • Scroll Bar mode gives each window a scroll bar. It is enabled by default, but the scroll bar is only displayed on graphical terminals. See Scroll Bars. • Tool Bar mode gives each frame a tool bar. It is enabled by default, but the tool bar is only displayed on graphical terminals. See Tool Bars. • Transient Mark mode highlights the region, and makes many Emacs commands operate on the region when the mark is active. It is enabled by default. See Mark. ## Choosing File Modes When you visit a file, Emacs chooses a major mode automatically. Normally, it makes the choice based on the file name—for example, files whose names end in '.c' are normally edited in C mode—but sometimes it chooses the major mode based on special text in the file. This special text can also be used to enable buffer-local minor modes. Here is the exact procedure: First, Emacs checks whether the file contains file-local mode variables. See File Variables. If there is a file-local variable that specifies a major mode, then Emacs uses that major mode, ignoring all other criteria. There are several methods to specify a major mode using a file-local variable; the simplest is to put the mode name in the first nonblank line, preceded and followed by '-*-'. Other text may appear on the line as well. For example, ; -*-Lisp-*-  tells Emacs to use Lisp mode. Note how the semicolon is used to make Lisp treat this line as a comment. You could equivalently write ; -*- mode: Lisp;-*-  You can also use file-local variables to specify buffer-local minor modes, by using eval specifications. For example, this first nonblank line puts the buffer in Lisp mode and enables Auto-Fill mode: ; -*- mode: Lisp; eval: (auto-fill-mode 1); -*-  Note, however, that it is usually inappropriate to enable minor modes this way, since most minor modes represent individual user preferences. If you personally want to use a minor mode for a particular file type, it is better to enable the minor mode via a major mode hook (see Major Modes). Second, if there is no file variable specifying a major mode, Emacs checks whether the file's contents begin with '#!'. If so, that indicates that the file can serve as an executable shell command, which works by running an interpreter named on the file's first line (the rest of the file is used as input to the interpreter). Therefore, Emacs tries to use the interpreter name to choose a mode. For instance, a file that begins with '#!/usr/bin/perl' is opened in Perl mode. The variable interpreter-mode-alist specifies the correspondence between interpreter program names and major modes. When the first line starts with '#!', you usually cannot use the '-*-' feature on the first line, because the system would get confused when running the interpreter. So Emacs looks for '-*-' on the second line in such files as well as on the first line. The same is true for man pages which start with the magic string ''\"' to specify a list of troff preprocessors. Third, Emacs tries to determine the major mode by looking at the text at the start of the buffer, based on the variable magic-mode-alist. By default, this variable is nil (an empty list), so Emacs skips this step; however, you can customize it in your init file (see Init File). The value should be a list of elements of the form (regexp . mode-function)  where regexp is a regular expression (see Regexps), and mode-function is a major mode command. If the text at the beginning of the file matches regexp, Emacs chooses the major mode specified by mode-function. Alternatively, an element of magic-mode-alist may have the form (match-function . mode-function)  where match-function is a Lisp function that is called at the beginning of the buffer; if the function returns non-nil, Emacs set the major mode with mode-function. Fourth—if Emacs still hasn't found a suitable major mode—it looks at the file's name. The correspondence between file names and major modes is controlled by the variable auto-mode-alist. Its value is a list in which each element has this form, (regexp . mode-function)  or this form, (regexp mode-function flag)  For example, one element normally found in the list has the form ("\\.c\\'" . c-mode), and it is responsible for selecting C mode for files whose names end in .c. (Note that '\\' is needed in Lisp syntax to include a '\' in the string, which must be used to suppress the special meaning of '.' in regexps.) If the element has the form (regexp mode-function flag) and flag is non-nil, then after calling mode-function, Emacs discards the suffix that matched regexp and searches the list again for another match. On GNU/Linux and other systems with case-sensitive file names, Emacs performs a case-sensitive search through auto-mode-alist; if this search fails, it performs a second case-insensitive search through the alist. To suppress the second search, change the variable auto-mode-case-fold to nil. On systems with case-insensitive file names, such as Microsoft Windows, Emacs performs a single case-insensitive search through auto-mode-alist. Finally, if Emacs still hasn't found a major mode to use, it compares the text at the start of the buffer to the variable magic-fallback-mode-alist. This variable works like magic-mode-alist, described above, except that is consulted only after auto-mode-alist. By default, magic-fallback-mode-alist contains forms that check for image files, HTML/XML/SGML files, and PostScript files. If you have changed the major mode of a buffer, you can return to the major mode Emacs would have chosen automatically, by typing M-x normal-mode. This is the same function that find-file calls to choose the major mode. It also processes the file's '-*-' line or local variables list (if any). See File Variables. The commands C-x C-w and set-visited-file-name change to a new major mode if the new file name implies a mode (see Saving). (C-x C-s does this too, if the buffer wasn't visiting a file.) However, this does not happen if the buffer contents specify a major mode, and certain "special" major modes do not allow the mode to change. You can turn off this mode-changing feature by setting change-major-mode-with-file-name to nil. ## Indentation Indentation refers to inserting or adjusting whitespace characters (space and/or tab characters) at the beginning of a line of text. This chapter documents indentation commands and options which are common to Text mode and related modes, as well as programming language modes. See Program Indent, for additional documentation about indenting in programming modes. The simplest way to perform indentation is the <TAB> key. In most major modes, this runs the command indent-for-tab-command. (In C and related modes, <TAB> runs the command c-indent-line-or-region, which behaves similarly).  Insert whitespace, or indent the current line, in a mode-appropriate way (indent-for-tab-command). If the region is active, indent all the lines within it. The exact behavior of <TAB> depends on the major mode. In Text mode and related major modes, <TAB> normally inserts some combination of space and tab characters to advance point to the next tab stop (see Tab Stops). For this purpose, the position of the first non-whitespace character on the preceding line is treated as an additional tab stop, so you can use <TAB> to "align" point with the preceding line. If the region is active (see Using Region), <TAB> acts specially: it indents each line in the region so that its first non-whitespace character is aligned with the preceding line. In programming modes, <TAB> indents the current line of code in a way that makes sense given the code in the preceding lines. If the region is active, all the lines in the region are indented this way. If point was initially within the current line's indentation, it is repositioned to the first non-whitespace character on the line. If you just want to insert a tab character in the buffer, type C-q <TAB> (see Inserting Text). ## Indentation Commands Apart from the <TAB> (indent-for-tab-command) command, Emacs provides a variety of commands to perform indentation in other ways.  C-j Perform followed by (newline-and-indent). C-M-o Split the current line at point (split-line). The text on the line after point becomes a new line, indented to the same column where point is located. This command first moves point forward over any spaces and tabs. Afterward, point is positioned before the inserted newline. M-m Move (forward or back) to the first non-whitespace character on the current line (back-to-indentation). If there are no non-whitespace characters on the line, move to the end of the line. M-i Indent whitespace at point, up to the next tab stop (tab-to-tab-stop). See Tab Stops. M-x indent-relative Insert whitespace at point, until point is aligned with the first non-whitespace character on the previous line (actually, the last non-blank line). If point is already farther right than that, run tab-to-tab-stop instead—unless called with a numeric argument, in which case do nothing. M-^ Merge the previous and the current line (delete-indentation). This "joins" the two lines cleanly, by replacing any indentation at the front of the current line, together with the line boundary, with a single space. As a special case (useful for Lisp code), the single space is omitted if the characters to be joined are consecutive opening and closing parentheses, or if the junction follows another newline. If there is a fill prefix, M-^ deletes the fill prefix if it appears after the newline that is deleted. See Fill Prefix. C-M-\ Indent all the lines in the region, as though you had typed at the beginning of each line (indent-region). If a numeric argument is supplied, indent every line in the region to that column number. C-x Shift each line in the region by a fixed distance, to the right or left (indent-rigidly). The distance to move is determined by the numeric argument (positive to move rightward, negative to move leftward). This command can be used to remove all indentation from the lines in the region, by invoking it with a large negative argument, e.g., C-u -1000 C-x . ## Tab Stops Emacs defines certain column numbers to be tab stops. These are used as stopping points by <TAB> when inserting whitespace in Text mode and related modes (see Indentation), and by commands like M-i (see Indentation Commands). By default, tab stops are located every 8 columns. These positions are stored in the variable tab-stop-list, whose value is a list of column numbers in increasing order. Instead of customizing the variable tab-stop-list directly, a convenient way to view and set tab stops is via the command M-x edit-tab-stops. This switches to a buffer containing a description of the tab stop settings, which looks like this:  : : : : : : 0 1 2 3 4 0123456789012345678901234567890123456789012345678 To install changes, type C-c C-c  The first line contains a colon at each tab stop. The numbers on the next two lines are present just to indicate where the colons are. You can edit this buffer to specify different tab stops by placing colons on the desired columns. The buffer uses Overwrite mode (see Minor Modes). When you are done, type C-c C-c to make the new tab stops take effect. Normally, the new tab stop settings apply to all buffers. However, if you have made the tab-stop-list variable local to the buffer where you called M-x edit-tab-stops (see Locals), then the new tab stop settings apply only to that buffer. To save the tab stop settings for future Emacs sessions, use the Customize interface to save the value of tab-stop-list (see Easy Customization). Note that the tab stops discussed in this section have nothing to do with how tab characters are displayed in the buffer. Tab characters are always displayed as empty spaces extending to the next display tab stop. See Text Display. ## Tabs Vs. Spaces Normally, indentation commands insert (or remove) an optimal mix of space characters and tab characters to align to the desired column. Tab characters are displayed as a stretch of empty space extending to the next display tab stop. By default, there is one display tab stop every tab-width columns (the default is 8). See Text Display. If you prefer, all indentation can be made from spaces only. To request this, set the buffer-local variable indent-tabs-mode to nil. See Locals, for information about setting buffer-local variables. Note, however, that C-q <TAB> always inserts a tab character, regardless of the value of indent-tabs-mode. One reason to set indent-tabs-mode to nil is that not all editors display tab characters in the same way. Emacs users, too, may have different customized values of tab-width. By using spaces only, you can make sure that your file always looks the same. If you only care about how it looks within Emacs, another way to tackle this problem is to set the tab-width variable in a file-local variable (see File Variables). There are also commands to convert tabs to spaces or vice versa, always preserving the columns of all non-whitespace text. M-x tabify scans the region for sequences of spaces, and converts sequences of at least two spaces to tabs if that can be done without changing indentation. M-x untabify changes all tabs in the region to appropriate numbers of spaces. ## Convenience Features for Indentation The variable tab-always-indent tweaks the behavior of the <TAB> (indent-for-tab-command) command. The default value, t, gives the behavior described in Indentation. If you change the value to the symbol complete, then <TAB> first tries to indent the current line, and if the line was already indented, it tries to complete the text at point (see Symbol Completion). If the value is nil, then <TAB> indents the current line only if point is at the left margin or in the line's indentation; otherwise, it inserts a tab character. Electric Indent mode is a global minor mode that automatically indents the line after every <RET> you type. To toggle this minor mode, type M-x electric-indent-mode. ## Commands For Human Languages This chapter describes Emacs commands that act on text, by which we mean sequences of characters in a human language (as opposed to, say, a computer programming language). These commands act in ways that take into account the syntactic and stylistic conventions of human languages: conventions involving words, sentences, paragraphs, and capital letters. There are also commands for filling, which means rearranging the lines of a paragraph to be approximately equal in length. These commands, while intended primarily for editing text, are also often useful for editing programs. Emacs has several major modes for editing human-language text. If the file contains ordinary text, use Text mode, which customizes Emacs in small ways for the syntactic conventions of text. Outline mode provides special commands for operating on text with an outline structure. Org mode extends Outline mode and turn Emacs into a full-fledged organizer: you can manage TODO lists, store notes and publish them in many formats. Emacs has other major modes for text which contains "embedded" commands, such as TeX and LaTeX (see TeX Mode); HTML and SGML (see HTML Mode); XML (see the nXML mode Info manual, which is distributed with Emacs); and Groff and Nroff (see Nroff Mode). If you need to edit pictures made out of text characters (commonly referred to as "ASCII art"), use Picture mode, a special major mode for editing such pictures. See Picture Mode. ## Words Emacs defines several commands for moving over or operating on words:  M-f Move forward over a word (forward-word). M-b Move backward over a word (backward-word). M-d Kill up to the end of a word (kill-word). M- Kill back to the beginning of a word (backward-kill-word). [email protected] Mark the end of the next word (mark-word). M-t Transpose two words or drag a word across others (transpose-words). Notice how these keys form a series that parallels the character-based C-f, C-b, C-d, <DEL> and C-t. [email protected] is cognate to [email protected], which is an alias for C-<SPC>. The commands M-f (forward-word) and M-b (backward-word) move forward and backward over words. These <Meta>-based key sequences are analogous to the key sequences C-f and C-b, which move over single characters. The analogy extends to numeric arguments, which serve as repeat counts. M-f with a negative argument moves backward, and M-b with a negative argument moves forward. Forward motion stops right after the last letter of the word, while backward motion stops right before the first letter. M-d (kill-word) kills the word after point. To be precise, it kills everything from point to the place M-f would move to. Thus, if point is in the middle of a word, M-d kills just the part after point. If some punctuation comes between point and the next word, it is killed along with the word. (If you wish to kill only the next word but not the punctuation before it, do M-f to get the end, and kill the word backwards with M-<DEL>.) M-d takes arguments just like M-f. M-<DEL> (backward-kill-word) kills the word before point. It kills everything from point back to where M-b would move to. For instance, if point is after the space in 'FOO, BAR', it kills 'FOO, '. If you wish to kill just 'FOO', and not the comma and the space, use M-b M-d instead of M-<DEL>. M-t (transpose-words) exchanges the word before or containing point with the following word. The delimiter characters between the words do not move. For example, 'FOO, BAR' transposes into 'BAR, FOO' rather than 'BAR FOO,'. See Transpose, for more on transposition. To operate on words with an operation which acts on the region, use the command [email protected] (mark-word). This command sets the mark where M-f would move to. See Marking Objects, for more information about this command. The word commands' understanding of word boundaries is controlled by the syntax table. Any character can, for example, be declared to be a word delimiter. Also, see Position Info for the M-= (count-words-region) and M-x count-words commands, which count and report the number of words in the region or buffer. ## Sentences The Emacs commands for manipulating sentences and paragraphs are mostly on Meta keys, like the word-handling commands.  M-a Move back to the beginning of the sentence (backward-sentence). M-e Move forward to the end of the sentence (forward-sentence). M-k Kill forward to the end of the sentence (kill-sentence). C-x Kill back to the beginning of the sentence (backward-kill-sentence). The commands M-a (backward-sentence) and M-e (forward-sentence) move to the beginning and end of the current sentence, respectively. Their bindings were chosen to resemble C-a and C-e, which move to the beginning and end of a line. Unlike them, M-a and M-e move over successive sentences if repeated. Moving backward over a sentence places point just before the first character of the sentence; moving forward places point right after the punctuation that ends the sentence. Neither one moves over the whitespace at the sentence boundary. Just as C-a and C-e have a kill command, C-k, to go with them, M-a and M-e have a corresponding kill command: M-k (kill-sentence) kills from point to the end of the sentence. With a positive numeric argument n, it kills the next n sentences; with a negative argument −n, it kills back to the beginning of the nth preceding sentence. The C-x <DEL> (backward-kill-sentence) kills back to the beginning of a sentence. The sentence commands assume that you follow the American typist's convention of putting two spaces at the end of a sentence. That is, a sentence ends wherever there is a '.', '?' or '!' followed by the end of a line or two spaces, with any number of ')', ']', ''', or '"' characters allowed in between. A sentence also begins or ends wherever a paragraph begins or ends. It is useful to follow this convention, because it allows the Emacs sentence commands to distinguish between periods that end a sentence and periods that indicate abbreviations. If you want to use just one space between sentences, you can set the variable sentence-end-double-space to nil to make the sentence commands stop for single spaces. However, this has a drawback: there is no way to distinguish between periods that end sentences and those that indicate abbreviations. For convenient and reliable editing, we therefore recommend you follow the two-space convention. The variable sentence-end-double-space also affects filling (see Fill Commands). The variable sentence-end controls how to recognize the end of a sentence. If non-nil, its value should be a regular expression, which is used to match the last few characters of a sentence, together with the whitespace following the sentence (see Regexps). If the value is nil, the default, then Emacs computes sentence ends according to various criteria such as the value of sentence-end-double-space. Some languages, such as Thai, do not use periods to indicate the end of a sentence. Set the variable sentence-end-without-period to t in such cases. ## Paragraphs The Emacs commands for manipulating paragraphs are also on Meta keys.  M-{ Move back to previous paragraph beginning (backward-paragraph). M-} Move forward to next paragraph end (forward-paragraph). M-h Put point and mark around this or next paragraph (mark-paragraph). M-{ (backward-paragraph) moves to the beginning of the current or previous paragraph (see below for the definition of a paragraph). M-} (forward-paragraph) moves to the end of the current or next paragraph. If there is a blank line before the paragraph, M-{ moves to the blank line. When you wish to operate on a paragraph, type M-h (mark-paragraph) to set the region around it. For example, M-h C-w kills the paragraph around or after point. M-h puts point at the beginning and mark at the end of the paragraph point was in. If point is between paragraphs (in a run of blank lines, or at a boundary), M-h sets the region around the paragraph following point. If there are blank lines preceding the first line of the paragraph, one of these blank lines is included in the region. If the region is already active, the command sets the mark without changing point, and each subsequent M-h further advances the mark by one paragraph. The definition of a paragraph depends on the major mode. In Fundamental mode, as well as Text mode and related modes, a paragraph is separated each neighboring paragraph another by one or more blank lines—lines that are either empty, or consist solely of space, tab and/or formfeed characters. In programming language modes, paragraphs are usually defined in a similar way, so that you can use the paragraph commands even though there are no paragraphs as such in a program. Note that an indented line is not itself a paragraph break in Text mode. If you want indented lines to separate paragraphs, use Paragraph-Indent Text mode instead. See Text Mode. If you set a fill prefix, then paragraphs are delimited by all lines which don't start with the fill prefix. See Filling. The precise definition of a paragraph boundary is controlled by the variables paragraph-separate and paragraph-start. The value of paragraph-start is a regular expression that should match lines that either start or separate paragraphs (see Regexps). The value of paragraph-separate is another regular expression that should match lines that separate paragraphs without being part of any paragraph (for example, blank lines). Lines that start a new paragraph and are contained in it must match only paragraph-start, not paragraph-separate. For example, in Fundamental mode, paragraph-start is "\f\\|[ \t]*", and paragraph-separate is "[ \t\f]*$". ## Pages Within some text files, text is divided into pages delimited by the formfeed character (ASCII code 12, also denoted as <control-L>), which is displayed in Emacs as the escape sequence '^L' (see Text Display). Traditionally, when such text files are printed to hardcopy, each formfeed character forces a page break. Most Emacs commands treat it just like any other character, so you can insert it with C-q C-l, delete it with <DEL>, etc. Also, Emacs provides commands to move over pages and operate on them.  M-x what-page Display the page number of point, and the line number within that page. C-x [ Move point to previous page boundary (backward-page). C-x ] Move point to next page boundary (forward-page). C-x C-p Put point and mark around this page (or another page) (mark-page). C-x l Count the lines in this page (count-lines-page). M-x what-page counts pages from the beginning of the file, and counts lines within the page, showing both numbers in the echo area. The C-x [ (backward-page) command moves point to immediately after the previous page delimiter. If point is already right after a page delimiter, it skips that one and stops at the previous one. A numeric argument serves as a repeat count. The C-x ] (forward-page) command moves forward past the next page delimiter. The C-x C-p command (mark-page) puts point at the beginning of the current page (after that page delimiter at the front), and the mark at the end of the page (after the page delimiter at the end). C-x C-p C-w is a handy way to kill a page to move it elsewhere. If you move to another page delimiter with C-x [ and C-x ], then yank the killed page, all the pages will be properly delimited once again. The reason C-x C-p includes only the following page delimiter in the region is to ensure that. A numeric argument to C-x C-p specifies which page to go to, relative to the current one. Zero means the current page, one the next page, and −1 the previous one. The C-x l command (count-lines-page) is good for deciding where to break a page in two. It displays in the echo area the total number of lines in the current page, and then divides it up into those preceding the current line and those following, as in Page has 96 (72+25) lines  Notice that the sum is off by one; this is correct if point is not at the beginning of a line. The variable page-delimiter controls where pages begin. Its value is a regular expression that matches the beginning of a line that separates pages (see Regexps). The normal value of this variable is "^\f", which matches a formfeed character at the beginning of a line. ## Filling Text Filling text means breaking it up into lines that fit a specified width. Emacs does filling in two ways. In Auto Fill mode, inserting text with self-inserting characters also automatically fills it. There are also explicit fill commands that you can use when editing text. • Auto Fill: Auto Fill mode breaks long lines automatically. • Fill Commands: Commands to refill paragraphs and center lines. • Fill Prefix: Filling paragraphs that are indented or in a comment, etc. • Adaptive Fill: How Emacs can determine the fill prefix automatically. ## Auto Fill Mode Auto Fill mode is a buffer-local minor mode (see Minor Modes) in which lines are broken automatically when they become too wide. Breaking happens only when you type a <SPC> or <RET>.  M-x auto-fill-mode Enable or disable Auto Fill mode. , In Auto Fill mode, break lines when appropriate. The mode command M-x auto-fill-mode toggles Auto Fill mode in the current buffer. With a positive numeric argument, it enables Auto Fill mode, and with a negative argument it disables it. If auto-fill-mode is called from Lisp with an omitted or nil argument, it enables Auto Fill mode. To enable Auto Fill mode automatically in certain major modes, add auto-fill-mode to the mode hooks (see Major Modes). When Auto Fill mode is enabled, the mode indicator 'Fill' appears in the mode line (see Mode Line). Auto Fill mode breaks lines automatically at spaces whenever they get longer than the desired width. This line breaking occurs only when you type <SPC> or <RET>. If you wish to insert a space or newline without permitting line-breaking, type C-q <SPC> or C-q C-j respectively. Also, C-o inserts a newline without line breaking. When Auto Fill mode breaks a line, it tries to obey the adaptive fill prefix: if a fill prefix can be deduced from the first and/or second line of the current paragraph, it is inserted into the new line (see Adaptive Fill). Otherwise, the new line is indented, as though you had typed <TAB> on it (see Indentation). In a programming language mode, if a line is broken in the middle of a comment, the comment is split by inserting new comment delimiters as appropriate. Auto Fill mode does not refill entire paragraphs; it breaks lines but does not merge lines. Therefore, editing in the middle of a paragraph can result in a paragraph that is not correctly filled. To fill it, call the explicit fill commands (see Fill Commands). ## Explicit Fill Commands  M-q Fill current paragraph (fill-paragraph). C-x f Set the fill column (set-fill-column). M-x fill-region Fill each paragraph in the region (fill-region). M-x fill-region-as-paragraph Fill the region, considering it as one paragraph. M-o M-s Center a line. The command M-q (fill-paragraph) fills the current paragraph. It redistributes the line breaks within the paragraph, and deletes any excess space and tab characters occurring within the paragraph, in such a way that the lines end up fitting within a certain maximum width. Normally, M-q acts on the paragraph where point is, but if point is between paragraphs, it acts on the paragraph after point. If the region is active, it acts instead on the text in the region. You can also call M-x fill-region to specifically fill the text in the region. M-q and fill-region use the usual Emacs criteria for finding paragraph boundaries (see Paragraphs). For more control, you can use M-x fill-region-as-paragraph, which refills everything between point and mark as a single paragraph. This command deletes any blank lines within the region, so separate blocks of text end up combined into one block. A numeric argument to M-q tells it to justify the text as well as filling it. This means that extra spaces are inserted to make the right margin line up exactly at the fill column. To remove the extra spaces, use M-q with no argument. (Likewise for fill-region.) The maximum line width for filling is specified by the buffer-local variable fill-column. The default value (see Locals) is 70. The easiest way to set fill-column in the current buffer is to use the command C-x f (set-fill-column). With a numeric argument, it uses that as the new fill column. With just C-u as argument, it sets fill-column to the current horizontal position of point. The command M-o M-s (center-line) centers the current line within the current fill column. With an argument n, it centers n lines individually and moves past them. This binding is made by Text mode and is available only in that and related modes (see Text Mode). By default, Emacs considers a period followed by two spaces or by a newline as the end of a sentence; a period followed by just one space indicates an abbreviation, not the end of a sentence. Accordingly, the fill commands will not break a line after a period followed by just one space. If you set the variable sentence-end-double-space to nil, the fill commands will break a line after a period followed by one space, and put just one space after each period. See Sentences, for other effects and possible drawbacks of this. If the variable colon-double-space is non-nil, the fill commands put two spaces after a colon. To specify additional conditions where line-breaking is not allowed, customize the abnormal hook variable fill-nobreak-predicate (see Hooks). Each function in this hook is called with no arguments, with point positioned where Emacs is considering breaking a line. If a function returns a non-nil value, Emacs will not break the line there. Two functions you can use are fill-single-word-nobreak-p (don't break after the first word of a sentence or before the last) and fill-french-nobreak-p (don't break after '(' or before ')', ':' or '?'). ## The Fill Prefix The fill prefix feature allows paragraphs to be filled so that each line starts with a special string of characters (such as a sequence of spaces, giving an indented paragraph). You can specify a fill prefix explicitly; otherwise, Emacs tries to deduce one automatically (see Adaptive Fill).  C-x . Set the fill prefix (set-fill-prefix). M-q Fill a paragraph using current fill prefix (fill-paragraph). M-x fill-individual-paragraphs Fill the region, considering each change of indentation as starting a new paragraph. M-x fill-nonuniform-paragraphs Fill the region, considering only paragraph-separator lines as starting a new paragraph. To specify a fill prefix for the current buffer, move to a line that starts with the desired prefix, put point at the end of the prefix, and type C-x . (set-fill-prefix). (That's a period after the C-x.) To turn off the fill prefix, specify an empty prefix: type C-x . with point at the beginning of a line. When a fill prefix is in effect, the fill commands remove the fill prefix from each line of the paragraph before filling, and insert it on each line after filling. (The beginning of the first line of the paragraph is left unchanged, since often that is intentionally different.) Auto Fill mode also inserts the fill prefix automatically when it makes a new line (see Auto Fill). The C-o command inserts the fill prefix on new lines it creates, when you use it at the beginning of a line (see Blank Lines). Conversely, the command M-^ deletes the prefix (if it occurs) after the newline that it deletes (see Indentation). For example, if fill-column is 40 and you set the fill prefix to ';; ', then M-q in the following text ;; This is an ;; example of a paragraph ;; inside a Lisp-style comment.  produces this: ;; This is an example of a paragraph ;; inside a Lisp-style comment.  Lines that do not start with the fill prefix are considered to start paragraphs, both in M-q and the paragraph commands; this gives good results for paragraphs with hanging indentation (every line indented except the first one). Lines which are blank or indented once the prefix is removed also separate or start paragraphs; this is what you want if you are writing multi-paragraph comments with a comment delimiter on each line. You can use M-x fill-individual-paragraphs to set the fill prefix for each paragraph automatically. This command divides the region into paragraphs, treating every change in the amount of indentation as the start of a new paragraph, and fills each of these paragraphs. Thus, all the lines in one "paragraph" have the same amount of indentation. That indentation serves as the fill prefix for that paragraph. M-x fill-nonuniform-paragraphs is a similar command that divides the region into paragraphs in a different way. It considers only paragraph-separating lines (as defined by paragraph-separate) as starting a new paragraph. Since this means that the lines of one paragraph may have different amounts of indentation, the fill prefix used is the smallest amount of indentation of any of the lines of the paragraph. This gives good results with styles that indent a paragraph's first line more or less that the rest of the paragraph. The fill prefix is stored in the variable fill-prefix. Its value is a string, or nil when there is no fill prefix. This is a per-buffer variable; altering the variable affects only the current buffer, but there is a default value which you can change as well. See Locals. The indentation text property provides another way to control the amount of indentation paragraphs receive. See Enriched Indentation. ## Adaptive Filling The fill commands can deduce the proper fill prefix for a paragraph automatically in certain cases: either whitespace or certain punctuation characters at the beginning of a line are propagated to all lines of the paragraph. If the paragraph has two or more lines, the fill prefix is taken from the paragraph's second line, but only if it appears on the first line as well. If a paragraph has just one line, fill commands may take a prefix from that line. The decision is complicated because there are three reasonable things to do in such a case: • Use the first line's prefix on all the lines of the paragraph. • Indent subsequent lines with whitespace, so that they line up under the text that follows the prefix on the first line, but don't actually copy the prefix from the first line. • Don't do anything special with the second and following lines. All three of these styles of formatting are commonly used. So the fill commands try to determine what you would like, based on the prefix that appears and on the major mode. Here is how. If the prefix found on the first line matches adaptive-fill-first-line-regexp, or if it appears to be a comment-starting sequence (this depends on the major mode), then the prefix found is used for filling the paragraph, provided it would not act as a paragraph starter on subsequent lines. Otherwise, the prefix found is converted to an equivalent number of spaces, and those spaces are used as the fill prefix for the rest of the lines, provided they would not act as a paragraph starter on subsequent lines. In Text mode, and other modes where only blank lines and page delimiters separate paragraphs, the prefix chosen by adaptive filling never acts as a paragraph starter, so it can always be used for filling. The variable adaptive-fill-regexp determines what kinds of line beginnings can serve as a fill prefix: any characters at the start of the line that match this regular expression are used. If you set the variable adaptive-fill-mode to nil, the fill prefix is never chosen automatically. You can specify more complex ways of choosing a fill prefix automatically by setting the variable adaptive-fill-function to a function. This function is called with point after the left margin of a line, and it should return the appropriate fill prefix based on that line. If it returns nil, adaptive-fill-regexp gets a chance to find a prefix. ## Case Conversion Commands Emacs has commands for converting either a single word or any arbitrary range of text to upper case or to lower case.  M-l Convert following word to lower case (downcase-word). M-u Convert following word to upper case (upcase-word). M-c Capitalize the following word (capitalize-word). C-x C-l Convert region to lower case (downcase-region). C-x C-u Convert region to upper case (upcase-region). M-l (downcase-word) converts the word after point to lower case, moving past it. Thus, repeating M-l converts successive words. M-u (upcase-word) converts to all capitals instead, while M-c (capitalize-word) puts the first letter of the word into upper case and the rest into lower case. All these commands convert several words at once if given an argument. They are especially convenient for converting a large amount of text from all upper case to mixed case, because you can move through the text using M-l, M-u or M-c on each word as appropriate, occasionally using M-f instead to skip a word. When given a negative argument, the word case conversion commands apply to the appropriate number of words before point, but do not move point. This is convenient when you have just typed a word in the wrong case: you can give the case conversion command and continue typing. If a word case conversion command is given in the middle of a word, it applies only to the part of the word which follows point. (This is comparable to what M-d (kill-word) does.) With a negative argument, case conversion applies only to the part of the word before point. The other case conversion commands are C-x C-u (upcase-region) and C-x C-l (downcase-region), which convert everything between point and mark to the specified case. Point and mark do not move. The region case conversion commands upcase-region and downcase-region are normally disabled. This means that they ask for confirmation if you try to use them. When you confirm, you may enable the command, which means it will not ask for confirmation again. See Disabling. ## Text Mode Text mode is a major mode for editing files of text in a human language. Files which have names ending in the extension .txt are usually opened in Text mode (see Choosing Modes). To explicitly switch to Text mode, type M-x text-mode. In Text mode, only blank lines and page delimiters separate paragraphs. As a result, paragraphs can be indented, and adaptive filling determines what indentation to use when filling a paragraph. See Adaptive Fill. In Text mode, the <TAB> (indent-for-tab-command) command usually inserts whitespace up to the next tab stop, instead of indenting the current line. See Indentation, for details. Text mode turns off the features concerned with comments except when you explicitly invoke them. It changes the syntax table so that single-quotes are considered part of words (e.g., 'don't' is considered one word). However, if a word starts with a single-quote, it is treated as a prefix for the purposes of capitalization (e.g., M-c converts ''hello'' into ''Hello'', as expected). If you indent the first lines of paragraphs, then you should use Paragraph-Indent Text mode (M-x paragraph-indent-text-mode) rather than Text mode. In that mode, you do not need to have blank lines between paragraphs, because the first-line indentation is sufficient to start a paragraph; however paragraphs in which every line is indented are not supported. Use M-x paragraph-indent-minor-mode to enable an equivalent minor mode for situations where you shouldn't change the major mode—in mail composition, for instance. Text mode binds M-<TAB> to ispell-complete-word. This command performs completion of the partial word in the buffer before point, using the spelling dictionary as the space of possible words. See Spelling. If your window manager defines M-<TAB> to switch windows, you can type <ESC> <TAB> or C-M-i instead. Entering Text mode runs the mode hook text-mode-hook (see Major Modes). The following sections describe several major modes that are derived from Text mode. These derivatives share most of the features of Text mode described above. In particular, derivatives of Text mode run text-mode-hook prior to running their own mode hooks. ## Outline Mode Outline mode is a major mode derived from Text mode, which is specialized for editing outlines. It provides commands to navigate between entries in the outline structure, and commands to make parts of a buffer temporarily invisible, so that the outline structure may be more easily viewed. Type M-x outline-mode to switch to Outline mode. Entering Outline mode runs the hook text-mode-hook followed by the hook outline-mode-hook (see Hooks). When you use an Outline mode command to make a line invisible (see Outline Visibility), the line disappears from the screen. An ellipsis (three periods in a row) is displayed at the end of the previous visible line, to indicate the hidden text. Multiple consecutive invisible lines produce just one ellipsis. Editing commands that operate on lines, such as C-n and C-p, treat the text of the invisible line as part of the previous visible line. Killing the ellipsis at the end of a visible line really kills all the following invisible text associated with the ellipsis. Outline minor mode is a buffer-local minor mode which provides the same commands as the major mode, Outline mode, but can be used in conjunction with other major modes. You can type M-x outline-minor-mode to toggle Outline minor mode in the current buffer, or use a file-local variable setting to enable it in a specific file (see File Variables). The major mode, Outline mode, provides special key bindings on the C-c prefix. Outline minor mode provides similar bindings with C-c @ as the prefix; this is to reduce the conflicts with the major mode's special commands. (The variable outline-minor-mode-prefix controls the prefix used.) ## Format of Outlines Outline mode assumes that the lines in the buffer are of two types: heading lines and body lines. A heading line represents a topic in the outline. Heading lines start with one or more asterisk ('*') characters; the number of asterisks determines the depth of the heading in the outline structure. Thus, a heading line with one '*' is a major topic; all the heading lines with two '*'s between it and the next one-'*' heading are its subtopics; and so on. Any line that is not a heading line is a body line. Body lines belong with the preceding heading line. Here is an example:  * Food This is the body, which says something about the topic of food. ** Delicious Food This is the body of the second-level header. ** Distasteful Food This could have a body too, with several lines. *** Dormitory Food * Shelter Another first-level topic with its header line.  A heading line together with all following body lines is called collectively an entry. A heading line together with all following deeper heading lines and their body lines is called a subtree. You can customize the criterion for distinguishing heading lines by setting the variable outline-regexp. (The recommended ways to do this are in a major mode function or with a file local variable.) Any line whose beginning has a match for this regexp is considered a heading line. Matches that start within a line (not at the left margin) do not count. The length of the matching text determines the level of the heading; longer matches make a more deeply nested level. Thus, for example, if a text formatter has commands '@chapter', '@section' and '@subsection' to divide the document into chapters and sections, you could make those lines count as heading lines by setting outline-regexp to '"@chap\\|@\$$sub\$$*section"'. Note the trick: the two words 'chapter' and 'section' are equally long, but by defining the regexp to match only 'chap' we ensure that the length of the text matched on a chapter heading is shorter, so that Outline mode will know that sections are contained in chapters. This works as long as no other command starts with '@chap'. You can explicitly specify a rule for calculating the level of a heading line by setting the variable outline-level. The value of outline-level should be a function that takes no arguments and returns the level of the current heading. The recommended ways to set this variable are in a major mode command or with a file local variable. ## Outline Motion Commands Outline mode provides special motion commands that move backward and forward to heading lines.  C-c C-n Move point to the next visible heading line (outline-next-visible-heading). C-c C-p Move point to the previous visible heading line (outline-previous-visible-heading). C-c C-f Move point to the next visible heading line at the same level as the one point is on (outline-forward-same-level). C-c C-b Move point to the previous visible heading line at the same level (outline-backward-same-level). C-c C-u Move point up to a lower-level (more inclusive) visible heading line (outline-up-heading). C-c C-n (outline-next-visible-heading) moves down to the next heading line. C-c C-p (outline-previous-visible-heading) moves similarly backward. Both accept numeric arguments as repeat counts. C-c C-f (outline-forward-same-level) and C-c C-b (outline-backward-same-level) move from one heading line to another visible heading at the same depth in the outline. C-c C-u (outline-up-heading) moves backward to another heading that is less deeply nested. ## Outline Visibility Commands Outline mode provides several commands for temporarily hiding or revealing parts of the buffer, based on the outline structure. These commands are not undoable; their effects are not recorded by the undo mechanism, so you can undo right past them (see Undo). Many of these commands act on the "current" heading line. If point is on a heading line, that is the current heading line; if point is on a body line, the current heading line is the nearest preceding header line.  C-c C-c Make the current heading line's body invisible (hide-entry). C-c C-e Make the current heading line's body visible (show-entry). C-c C-d Make everything under the current heading invisible, not including the heading itself (hide-subtree). C-c C-s Make everything under the current heading visible, including body, subheadings, and their bodies (show-subtree). C-c C-l Make the body of the current heading line, and of all its subheadings, invisible (hide-leaves). C-c C-k Make all subheadings of the current heading line, at all levels, visible (show-branches). C-c C-i Make immediate subheadings (one level down) of the current heading line visible (show-children). C-c C-t Make all body lines in the buffer invisible (hide-body). C-c C-a Make all lines in the buffer visible (show-all). C-c C-q Hide everything except the top n levels of heading lines (hide-sublevels). C-c C-o Hide everything except for the heading or body that point is in, plus the headings leading up from there to the top level of the outline (hide-other). The simplest of these commands are C-c C-c (hide-entry), which hides the body lines directly following the current heading line, and C-c C-e (show-entry), which reveals them. Subheadings and their bodies are not affected. The commands C-c C-d (hide-subtree) and C-c C-s (show-subtree) are more powerful. They apply to the current heading line's subtree: its body, all of its subheadings, both direct and indirect, and all of their bodies. The command C-c C-l (hide-leaves) hides the body of the current heading line as well as all the bodies in its subtree; the subheadings themselves are left visible. The command C-c C-k (show-branches) reveals the subheadings, if they had previously been hidden (e.g., by C-c C-d). The command C-c C-i (show-children) is a weaker version of this; it reveals just the direct subheadings, i.e., those one level down. The command C-c C-o (hide-other) hides everything except the entry that point is in, plus its parents (the headers leading up from there to top level in the outline) and the top level headings. The remaining commands affect the whole buffer. C-c C-t (hide-body) makes all body lines invisible, so that you see just the outline structure (as a special exception, it will not hide lines at the top of the file, preceding the first header line, even though these are technically body lines). C-c C-a (show-all) makes all lines visible. C-c C-q (hide-sublevels) hides all but the top level headings; with a numeric argument n, it hides everything except the top n levels of heading lines. When incremental search finds text that is hidden by Outline mode, it makes that part of the buffer visible. If you exit the search at that position, the text remains visible. You can also automatically make text visible as you navigate in it by using Reveal mode (M-x reveal-mode), a buffer-local minor mode. ## Viewing One Outline in Multiple Views You can display two views of a single outline at the same time, in different windows. To do this, you must create an indirect buffer using M-x make-indirect-buffer. The first argument of this command is the existing outline buffer name, and its second argument is the name to use for the new indirect buffer. See Indirect Buffers. Once the indirect buffer exists, you can display it in a window in the normal fashion, with C-x 4 b or other Emacs commands. The Outline mode commands to show and hide parts of the text operate on each buffer independently; as a result, each buffer can have its own view. If you want more than two views on the same outline, create additional indirect buffers. ## Folding Editing The Foldout package extends Outline mode and Outline minor mode with "folding" commands. The idea of folding is that you zoom in on a nested portion of the outline, while hiding its relatives at higher levels. Consider an Outline mode buffer with all the text and subheadings under level-1 headings hidden. To look at what is hidden under one of these headings, you could use C-c C-e (M-x show-entry) to expose the body, or C-c C-i to expose the child (level-2) headings. With Foldout, you use C-c C-z (M-x foldout-zoom-subtree). This exposes the body and child subheadings, and narrows the buffer so that only the level-1 heading, the body and the level-2 headings are visible. Now to look under one of the level-2 headings, position the cursor on it and use C-c C-z again. This exposes the level-2 body and its level-3 child subheadings and narrows the buffer again. Zooming in on successive subheadings can be done as much as you like. A string in the mode line shows how deep you've gone. When zooming in on a heading, to see only the child subheadings specify a numeric argument: C-u C-c C-z. The number of levels of children can be specified too (compare M-x show-children), e.g., M-2 C-c C-z exposes two levels of child subheadings. Alternatively, the body can be specified with a negative argument: M-- C-c C-z. The whole subtree can be expanded, similarly to C-c C-s (M-x show-subtree), by specifying a zero argument: M-0 C-c C-z. While you're zoomed in, you can still use Outline mode's exposure and hiding functions without disturbing Foldout. Also, since the buffer is narrowed, "global" editing actions will only affect text under the zoomed-in heading. This is useful for restricting changes to a particular chapter or section of your document. To unzoom (exit) a fold, use C-c C-x (M-x foldout-exit-fold). This hides all the text and subheadings under the top-level heading and returns you to the previous view of the buffer. Specifying a numeric argument exits that many levels of folds. Specifying a zero argument exits all folds. To cancel the narrowing of a fold without hiding the text and subheadings, specify a negative argument. For example, M--2 C-c C-x exits two folds and leaves the text and subheadings exposed. Foldout mode also provides mouse commands for entering and exiting folds, and for showing and hiding text:  C-M-Mouse-1 zooms in on the heading clicked on: single click: expose body. double click: expose subheadings. triple click: expose body and subheadings. quad click: expose entire subtree. C-M-Mouse-2 exposes text under the heading clicked on: single click: expose body. double click: expose subheadings. triple click: expose body and subheadings. quad click: expose entire subtree. C-M-Mouse-3 hides text under the heading clicked on or exits fold: single click: hide subtree. double click: exit fold and hide text. triple click: exit fold without hiding text. quad click: exit all folds and hide text. You can specify different modifier keys (instead of Control-Meta-) by setting foldout-mouse-modifiers; but if you have already loaded the foldout.el library, you must reload it in order for this to take effect. To use the Foldout package, you can type M-x load-library <RET> foldout <RET>; or you can arrange for to do that automatically by putting the following in your init file: (eval-after-load "outline" '(require 'foldout))  ## Org Mode Org mode is a variant of Outline mode for using Emacs as an organizer and/or authoring system. Files with names ending in the extension .org are opened in Org mode (see Choosing Modes). To explicitly switch to Org mode, type M-x org-mode. In Org mode, as in Outline mode, each entry has a heading line that starts with one or more '*' characters. See Outline Format. Also, any line that begins with the '#' character is treated as a comment. Org mode provides commands for easily viewing and manipulating the outline structure. The simplest of these commands is <TAB> (org-cycle). If invoked on a heading line, it cycles through the different visibility states of the subtree: (i) showing only that heading line, (ii) showing only the heading line and the heading lines of its direct children, if any, and (iii) showing the entire subtree. If invoked in a body line, the global binding for <TAB> is executed. Typing <S-TAB> (org-shifttab) anywhere in an Org mode buffer cycles the visibility of the entire outline structure, between (i) showing only top-level heading lines, (ii) showing all heading lines but no body lines, and (iii) showing everything. You can move an entire entry up or down in the buffer, including its body lines and subtree (if any), by typing M-<up> (org-metaup) or M-<down> (org-metadown) on the heading line. Similarly, you can promote or demote a heading line with M-<left> (org-metaleft) and M-<right> (org-metaright). These commands execute their global bindings if invoked on a body line. The following subsections give basic instructions for using Org mode as an organizer and as an authoring system. ## Org as an Organizer You can tag an Org entry as a TODO item by typing C-c C-t (org-todo) anywhere in the entry. This adds the keyword 'TODO' to the heading line. Typing C-c C-t again switches the keyword to 'DONE'; another C-c C-t removes the keyword entirely, and so forth. You can customize the keywords used by C-c C-t via the variable org-todo-keywords. Apart from marking an entry as TODO, you can attach a date to it, by typing C-c C-s (org-schedule) in the entry. This prompts for a date by popping up the Emacs Calendar (see Calendar/Diary), and then adds the tag 'SCHEDULED', together with the selected date, beneath the heading line. The command C-c C-d (org-deadline) has the same effect, except that it uses the tag DEADLINE. Once you have some TODO items planned in an Org file, you can add that file to the list of agenda files by typing C-c [ (org-agenda-file-to-front). Org mode is designed to let you easily maintain multiple agenda files, e.g., for organizing different aspects of your life. The list of agenda files is stored in the variable org-agenda-files. To view items coming from your agenda files, type M-x org-agenda. This command prompts for what you want to see: a list of things to do this week, a list of TODO items with specific keywords, etc. ## Org as an Authoring System You may want to format your Org notes nicely and to prepare them for export and publication. To export the current buffer, type C-c C-e (org-export) anywhere in an Org buffer. This command prompts for an export format; currently supported formats include HTML, LaTeX, OpenDocument (.odt), and PDF. Some formats, such as PDF, require certain system tools to be installed. To export several files at once to a specific directory, either locally or over the network, you must define a list of projects through the variable org-publish-project-alist. See its documentation for details. Org supports a simple markup scheme for applying text formatting to exported documents: - This text is /emphasized/ - This text is *in bold* - This text is _underlined_ - This text uses =a teletype font= #+begin_quote This is a quote.'' #+end_quote #+begin_example This is an example. #+end_example  ## TeX Mode Emacs provides special major modes for editing files written in TeX and its related formats. TeX is a powerful text formatter written by Donald Knuth; like GNU Emacs, it is free software. LaTeX is a simplified input format for TeX, implemented using TeX macros. DocTeX is a special file format in which the LaTeX sources are written, combining sources with documentation. SliTeX is an obsolete special form of LaTeX. TeX mode has four variants: Plain TeX mode, LaTeX mode, DocTeX mode, and SliTeX mode. These distinct major modes differ only slightly, and are designed for editing the four different formats. Emacs selects the appropriate mode by looking at the contents of the buffer. (This is done by the tex-mode command, which is normally called automatically when you visit a TeX-like file. See Choosing Modes.) If the contents are insufficient to determine this, Emacs chooses the mode specified by the variable tex-default-mode; its default value is latex-mode. If Emacs does not guess right, you can select the correct variant of TeX mode using the command M-x plain-tex-mode, M-x latex-mode, M-x slitex-mode, or doctex-mode. The following sections document the features of TeX mode and its variants. There are other TeX-related Emacs packages, which are not documented here: • BibTeX mode is a major mode for BibTeX files, which are commonly used for keeping bibliographic references for LaTeX documents. • The RefTeX package provides a minor mode which can be used with LaTeX mode to manage bibliographic references. For more information, see the RefTeX Info manual, which is distributed with Emacs. • The AUCTeX package provides more advanced features for editing TeX and its related formats, including the ability to preview TeX equations within Emacs buffers. Unlike BibTeX mode and the RefTeX package, AUCTeX is not distributed with Emacs by default. It can be downloaded via the Package Menu (see Packages); once installed, see the AUCTeX manual, which is included with the package. • TeX Editing: Special commands for editing in TeX mode. • LaTeX Editing: Additional commands for LaTeX input files. • TeX Print: Commands for printing part of a file with TeX. • TeX Misc: Customization of TeX mode, and related features. ## TeX Editing Commands  " Insert, according to context, either '' or '"' or '''' (tex-insert-quote). C-j Insert a paragraph break (two newlines) and check the previous paragraph for unbalanced braces or dollar signs (tex-terminate-paragraph). M-x tex-validate-region Check each paragraph in the region for unbalanced braces or dollar signs. C-c { Insert '{}' and position point between them (tex-insert-braces). C-c } Move forward past the next unmatched close brace (up-list). In TeX, the character '"' is not normally used; instead, quotations begin with '' and end with ''''. TeX mode therefore binds the " key to the tex-insert-quote command. This inserts '' after whitespace or an open brace, '"' after a backslash, and '''' after any other character. As a special exception, if you type " when the text before point is either '' or '''', Emacs replaces that preceding text with a single '"' character. You can therefore type "" to insert '"', should you ever need to do so. (You can also use C-q " to insert this character.) In TeX mode, '$' has a special syntax code which attempts to understand the way TeX math mode delimiters match. When you insert a '$' that is meant to exit math mode, the position of the matching '$' that entered math mode is displayed for a second. This is the same feature that displays the open brace that matches a close brace that is inserted. However, there is no way to tell whether a '$' enters math mode or leaves it; so when you insert a '$' that enters math mode, the previous '' position is shown as if it were a match, even though they are actually unrelated. TeX uses braces as delimiters that must match. Some users prefer to keep braces balanced at all times, rather than inserting them singly. Use C-c { (tex-insert-braces) to insert a pair of braces. It leaves point between the two braces so you can insert the text that belongs inside. Afterward, use the command C-c } (up-list) to move forward past the close brace. There are two commands for checking the matching of braces. C-j (tex-terminate-paragraph) checks the paragraph before point, and inserts two newlines to start a new paragraph. It outputs a message in the echo area if any mismatch is found. M-x tex-validate-region checks a region, paragraph by paragraph. The errors are listed in an *Occur* buffer; you can use the usual Occur mode commands in that buffer, such as C-c C-c, to visit a particular mismatch (see Other Repeating Search). Note that Emacs commands count square brackets and parentheses in TeX mode, not just braces. This is not strictly correct for the purpose of checking TeX syntax. However, parentheses and square brackets are likely to be used in text as matching delimiters, and it is useful for the various motion commands and automatic match display to work with them. ## LaTeX Editing Commands LaTeX mode provides a few extra features not applicable to plain TeX:  C-c C-o Insert '\begin' and '\end' for LaTeX block and position point on a line between them (tex-latex-block). C-c C-e Close the innermost LaTeX block not yet closed (tex-close-latex-block). In LaTeX input, '\begin' and '\end' tags are used to group blocks of text. To insert a block, type C-c C-o (tex-latex-block). This prompts for a block type, and inserts the appropriate matching '\begin' and '\end' tags, leaving a blank line between the two and moving point there. When entering the block type argument to C-c C-o, you can use the usual completion commands (see Completion). The default completion list contains the standard LaTeX block types. If you want additional block types for completion, customize the list variable latex-block-names. In LaTeX input, '\begin' and '\end' tags must balance. You can use C-c C-e (tex-close-latex-block) to insert an '\end' tag which matches the last unmatched '\begin'. It also indents the '\end' to match the corresponding '\begin', and inserts a newline after the '\end' tag if point is at the beginning of a line. The minor mode latex-electric-env-pair-mode automatically inserts an '\end' or '\begin' tag for you when you type the corresponding one. ## TeX Printing Commands You can invoke TeX as an subprocess of Emacs, supplying either the entire contents of the buffer or just part of it (e.g., one chapter of a larger document).  C-c C-b Invoke TeX on the entire current buffer (tex-buffer). C-c C-r Invoke TeX on the current region, together with the buffer's header (tex-region). C-c C-f Invoke TeX on the current file (tex-file). C-c C-v Preview the output from the last C-c C-r, C-c C-b, or C-c C-f command (tex-view). C-c C-p Print the output from the last C-c C-b, C-c C-r, or C-c C-f command (tex-print). C-c Invoke BibTeX on the current file (tex-bibtex-file). C-c C-l Recenter the window showing output from TeX so that the last line can be seen (tex-recenter-output-buffer). C-c C-k Kill the TeX subprocess (tex-kill-job). C-c C-c Invoke some other compilation command on the entire current buffer (tex-compile). To pass the current buffer through TeX, type C-c C-b (tex-buffer). The formatted output goes in a temporary file, normally a .dvi file. Afterwards, you can type C-c C-v (tex-view) to launch an external program, such as xdvi, to view this output file. You can also type C-c C-p (tex-print) to print a hardcopy of the output file. By default, C-c C-b runs TeX in the current directory. The output of TeX also goes in this directory. To run TeX in a different directory, change the variable tex-directory to the desired directory name. If your environment variable TEXINPUTS contains relative directory names, or if your files contains '\input' commands with relative file names, then tex-directory must be "." or you will get the wrong results. Otherwise, it is safe to specify some other directory, such as "/tmp". The buffer's TeX variant determines what shell command C-c C-b actually runs. In Plain TeX mode, it is specified by the variable tex-run-command, which defaults to "tex". In LaTeX mode, it is specified by latex-run-command, which defaults to "latex". The shell command that C-c C-v runs to view the .dvi output is determined by the variable tex-dvi-view-command, regardless of the TeX variant. The shell command that C-c C-p runs to print the output is determined by the variable tex-dvi-print-command. Normally, Emacs automatically appends the output file name to the shell command strings described in the preceding paragraph. For example, if tex-dvi-view-command is "xdvi", C-c C-v runs xdvi output-file-name. In some cases, however, the file name needs to be embedded in the command, e.g., if you need to provide the file name as an argument to one command whose output is piped to another. You can specify where to put the file name with '*' in the command string. For example, (setq tex-dvi-print-command "dvips -f * | lpr")  The terminal output from TeX, including any error messages, appears in a buffer called *tex-shell*. If TeX gets an error, you can switch to this buffer and feed it input (this works as in Shell mode; see Interactive Shell). Without switching to this buffer you can scroll it so that its last line is visible by typing C-c C-l. Type C-c C-k (tex-kill-job) to kill the TeX process if you see that its output is no longer useful. Using C-c C-b or C-c C-r also kills any TeX process still running. You can also pass an arbitrary region through TeX by typing C-c C-r (tex-region). This is tricky, however, because most files of TeX input contain commands at the beginning to set parameters and define macros, without which no later part of the file will format correctly. To solve this problem, C-c C-r allows you to designate a part of the file as containing essential commands; it is included before the specified region as part of the input to TeX. The designated part of the file is called the header. To indicate the bounds of the header in Plain TeX mode, you insert two special strings in the file. Insert '%**start of header' before the header, and '%**end of header' after it. Each string must appear entirely on one line, but there may be other text on the line before or after. The lines containing the two strings are included in the header. If '%**start of header' does not appear within the first 100 lines of the buffer, C-c C-r assumes that there is no header. In LaTeX mode, the header begins with '\documentclass' or '\documentstyle' and ends with '\begin{document}'. These are commands that LaTeX requires you to use in any case, so nothing special needs to be done to identify the header. The commands (tex-buffer) and (tex-region) do all of their work in a temporary directory, and do not have available any of the auxiliary files needed by TeX for cross-references; these commands are generally not suitable for running the final copy in which all of the cross-references need to be correct. When you want the auxiliary files for cross references, use C-c C-f (tex-file) which runs TeX on the current buffer's file, in that file's directory. Before running TeX, it offers to save any modified buffers. Generally, you need to use (tex-file) twice to get the cross-references right. The value of the variable tex-start-options specifies options for the TeX run. The value of the variable tex-start-commands specifies TeX commands for starting TeX. The default value causes TeX to run in nonstop mode. To run TeX interactively, set the variable to "". Large TeX documents are often split into several files—one main file, plus subfiles. Running TeX on a subfile typically does not work; you have to run it on the main file. To make tex-file useful when you are editing a subfile, you can set the variable tex-main-file to the name of the main file. Then tex-file runs TeX on that file. The most convenient way to use tex-main-file is to specify it in a local variable list in each of the subfiles. See File Variables. For LaTeX files, you can use BibTeX to process the auxiliary file for the current buffer's file. BibTeX looks up bibliographic citations in a data base and prepares the cited references for the bibliography section. The command C-c <TAB> (tex-bibtex-file) runs the shell command (tex-bibtex-command) to produce a '.bbl' file for the current buffer's file. Generally, you need to do C-c C-f (tex-file) once to generate the '.aux' file, then do C-c <TAB> (tex-bibtex-file), and then repeat C-c C-f (tex-file) twice more to get the cross-references correct. To invoke some other compilation program on the current TeX buffer, type C-c C-c (tex-compile). This command knows how to pass arguments to many common programs, including pdflatex, yap, xdvi, and dvips. You can select your desired compilation program using the standard completion keys (see Completion). ## Tex Mode Miscellany Entering any variant of TeX mode runs the hooks text-mode-hook and tex-mode-hook. Then it runs either plain-tex-mode-hook, latex-mode-hook, or slitex-mode-hook, whichever is appropriate. Starting the TeX shell runs the hook tex-shell-hook. See Hooks. The commands M-x iso-iso2tex, M-x iso-tex2iso, M-x iso-iso2gtex and M-x iso-gtex2iso can be used to convert between Latin-1 encoded files and TeX-encoded equivalents. ## SGML and HTML Modes The major modes for SGML and HTML provide indentation support and commands for operating on tags. HTML mode is a slightly customized variant of SGML mode.  C-c C-n Interactively specify a special character and insert the SGML '&'-command for that character (sgml-name-char). C-c C-t Interactively specify a tag and its attributes (sgml-tag). This command asks you for a tag name and for the attribute values, then inserts both the opening tag and the closing tag, leaving point between them. With a prefix argument n, the command puts the tag around the n words already present in the buffer after point. Whenever a region is active, it puts the tag around the region (when Transient Mark mode is off, it does this when a numeric argument of −1 is supplied.) C-c C-a Interactively insert attribute values for the current tag (sgml-attributes). C-c C-f Skip across a balanced tag group (which extends from an opening tag through its corresponding closing tag) (sgml-skip-tag-forward). A numeric argument acts as a repeat count. C-c C-b Skip backward across a balanced tag group (which extends from an opening tag through its corresponding closing tag) (sgml-skip-tag-backward). A numeric argument acts as a repeat count. C-c C-d Delete the tag at or after point, and delete the matching tag too (sgml-delete-tag). If the tag at or after point is an opening tag, delete the closing tag too; if it is a closing tag, delete the opening tag too. C-c ? tag Display a description of the meaning of tag tag (sgml-tag-help). If the argument tag is empty, describe the tag at point. C-c / Insert a close tag for the innermost unterminated tag (sgml-close-tag). If called within a tag or a comment, close it instead of inserting a close tag. C-c 8 Toggle a minor mode in which Latin-1 characters insert the corresponding SGML commands that stand for them, instead of the characters themselves (sgml-name-8bit-mode). C-c C-v Run a shell command (which you must specify) to validate the current buffer as SGML (sgml-validate). C-c TAB Toggle the visibility of existing tags in the buffer. This can be used as a cheap preview (sgml-tags-invisible). The major mode for editing XML documents is called nXML mode. This is a powerful major mode that can recognize many existing XML schema and use them to provide completion of XML elements via M-<TAB>, as well as "on-the-fly" XML validation with error highlighting. To enable nXML mode in an existing buffer, type M-x nxml-mode, or, equivalently, M-x xml-mode. Emacs uses nXML mode for files which have the extension .xml. For XHTML files, which have the extension .xhtml, Emacs uses HTML mode by default; you can make it use nXML mode by customizing the variable auto-mode-alist (see Choosing Modes). nXML mode is described in an Info manual, which is distributed with Emacs. You may choose to use the less powerful SGML mode for editing XML, since XML is a strict subset of SGML. To enable SGML mode in an existing buffer, type M-x sgml-mode. On enabling SGML mode, Emacs examines the buffer to determine whether it is XML; if so, it sets the variable sgml-xml-mode to a non-nil value. This causes SGML mode's tag insertion commands, described above, to always insert explicit closing tags as well. ## Nroff Mode Nroff mode, a major mode derived from Text mode, is specialized for editing nroff files (e.g., Unix man pages). Type M-x nroff-mode to enter this mode. Entering Nroff mode runs the hook text-mode-hook, then nroff-mode-hook (see Hooks). In Nroff mode, nroff command lines are treated as paragraph separators, pages are separated by '.bp' commands, and comments start with backslash-doublequote. It also defines these commands:  M-n Move to the beginning of the next line that isn't an nroff command (forward-text-line). An argument is a repeat count. M-p Like M-n but move up (backward-text-line). M-? Displays in the echo area the number of text lines (lines that are not nroff commands) in the region (count-text-lines). Electric Nroff mode is a buffer-local minor mode that can be used with Nroff mode. To toggle this minor mode, type M-x electric-nroff-mode (see Minor Modes). When the mode is on, each time you type <RET> to end a line containing an nroff command that opens a kind of grouping, the nroff command to close that grouping is automatically inserted on the following line. If you use Outline minor mode with Nroff mode (see Outline Mode), heading lines are lines of the form '.H' followed by a number (the header level). ## Enriched Text Enriched mode is a minor mode for editing formatted text files in a WYSIWYG ("what you see is what you get") fashion. When Enriched mode is enabled, you can apply various formatting properties to the text in the buffer, such as fonts and colors; upon saving the buffer, those properties are saved together with the text, using the MIME 'text/enriched' file format. Enriched mode is typically used with Text mode (see Text Mode). It is not compatible with Font Lock mode, which is used by many major modes, including most programming language modes, for syntax highlighting (see Font Lock). Unlike Enriched mode, Font Lock mode assigns text properties automatically, based on the current buffer contents; those properties are not saved to disk. The file etc/enriched.doc in the Emacs distribution serves as an example of the features of Enriched mode. ## Enriched Mode Enriched mode is a buffer-local minor mode (see Minor Modes). When you visit a file that has been saved in the 'text/enriched' format, Emacs automatically enables Enriched mode, and applies the formatting information in the file to the buffer text. When you save a buffer with Enriched mode enabled, it is saved using the 'text/enriched' format, including the formatting information. To create a new file of formatted text, visit the nonexistent file and type M-x enriched-mode. This command actually toggles Enriched mode. With a prefix argument, it enables Enriched mode if the argument is positive, and disables Enriched mode otherwise. If you disable Enriched mode, Emacs no longer saves the buffer using the 'text/enriched' format; any formatting properties that have been added to the buffer remain in the buffer, but they are not saved to disk. Enriched mode does not save all Emacs text properties, only those specified in the variable enriched-translations. These include properties for fonts, colors, indentation, and justification. If you visit a file and Emacs fails to recognize that it is in the 'text/enriched' format, type M-x format-decode-buffer. This command prompts for a file format, and re-reads the file in that format. Specifying the 'text/enriched' format automatically enables Enriched mode. To view a 'text/enriched' file in raw form (as plain text with markup tags rather than formatted text), use M-x find-file-literally (see Visiting). ## Hard and Soft Newlines In Enriched mode, Emacs distinguishes between two different kinds of newlines, hard newlines and soft newlines. You can also enable or disable this feature in other buffers, by typing M-x use-hard-newlines. Hard newlines are used to separate paragraphs, or anywhere there needs to be a line break regardless of how the text is filled; soft newlines are used for filling. The <RET> (newline) and C-o (open-line) commands insert hard newlines. The fill commands, including Auto Fill (see Auto Fill), insert only soft newlines and delete only soft newlines, leaving hard newlines alone. Thus, when editing with Enriched mode, you should not use <RET> or C-o to break lines in the middle of filled paragraphs. Use Auto Fill mode or explicit fill commands (see Fill Commands) instead. Use <RET> or C-o where line breaks should always remain, such as in tables and lists. For such lines, you may also want to set the justification style to unfilled (see Enriched Justification). ## Editing Format Information The easiest way to alter properties is with the Text Properties menu. You can get to this menu from the Edit menu in the menu bar (see Menu Bar), or with C-Mouse-2 (see Menu Mouse Clicks). Some of the commands in the Text Properties menu are listed below (you can also invoke them with M-x):  Remove Face Properties Remove face properties from the region (facemenu-remove-face-props). Remove Text Properties Remove all text properties from the region, including face properties (facemenu-remove-all). Describe Properties List all text properties and other information about the character following point (describe-text-properties). Display Faces Display a list of defined faces (list-faces-display). See Faces. Display Colors Display a list of defined colors (list-colors-display). See Colors. The other menu entries are described in the following sections. ## Faces in Enriched Text The following commands can be used to add or remove faces (see Faces). Each applies to the text in the region if the mark is active, and to the next self-inserting character if the mark is inactive. With a prefix argument, each command applies to the next self-inserting character even if the region is active.  M-o d Remove all face properties (facemenu-set-default). M-o b Apply the bold face (facemenu-set-bold). M-o i Apply the italic face (facemenu-set-italic). M-o l Apply the bold-italic face (facemenu-set-bold-italic). M-o u Apply the underline face (facemenu-set-underline). M-o o face Apply the face face (facemenu-set-face). M-x facemenu-set-foreground Prompt for a color (see Colors), and apply it as a foreground color. M-x facemenu-set-background Prompt for a color, and apply it as a background color. These command are also available via the Text Properties menu. A self-inserting character normally inherits the face properties (and most other text properties) from the preceding character in the buffer. If you use one of the above commands to specify the face for the next self-inserting character, that character will not inherit the faces properties from the preceding character, but it will still inherit other text properties. Enriched mode defines two additional faces: excerpt and fixed. These correspond to codes used in the text/enriched file format. The excerpt face is intended for quotations; by default, it appears the same as italic. The fixed face specifies fixed-width text; by default, it appears the same as bold. ## Indentation in Enriched Text In Enriched mode, you can specify different amounts of indentation for the right or left margin of a paragraph or a part of a paragraph. These margins also affect fill commands such as M-q (see Filling). The Indentation submenu of Text Properties offers commands for specifying indentation:  Indent More Indent the region by 4 columns (increase-left-margin). In Enriched mode, this command is also available on C-x ; if you supply a numeric argument, that says how many columns to add to the margin (a negative argument reduces the number of columns). Indent Less Remove 4 columns of indentation from the region. Indent Right More Make the text narrower by indenting 4 columns at the right margin. Indent Right Less Remove 4 columns of indentation from the right margin. The variable standard-indent specifies how many columns these commands should add to or subtract from the indentation. The default value is 4. The default right margin for Enriched mode is controlled by the variable fill-column, as usual. You can also type C-c [ (set-left-margin) and C-c ] (set-right-margin) to set the left and right margins. You can specify the margin width with a numeric argument; otherwise these commands prompt for a value via the minibuffer. The fill prefix, if any, works in addition to the specified paragraph indentation: C-x . does not include the specified indentation's whitespace in the new value for the fill prefix, and the fill commands look for the fill prefix after the indentation on each line. See Fill Prefix. ## Justification in Enriched Text In Enriched mode, you can use the following commands to specify various justification styles for filling. These commands apply to the paragraph containing point, or, if the region is active, to all paragraphs overlapping the region.  M-j l Align lines to the left margin (set-justification-left). M-j r Align lines to the right margin (set-justification-right). M-j b Align lines to both margins, inserting spaces in the middle of the line to achieve this (set-justification-full). M-j c, M-S Center lines between the margins (set-justification-center). M-j u Turn off filling entirely (set-justification-none). The fill commands do nothing on text with this setting. You can, however, still indent the left margin. You can also specify justification styles using the Justification submenu in the Text Properties menu. The default justification style is specified by the per-buffer variable default-justification. Its value should be one of the symbols left, right, full, center, or none. ## Setting Other Text Properties The Special Properties submenu of Text Properties has entries for adding or removing three other text properties: read-only, (which disallows alteration of the text), invisible (which hides text), and intangible (which disallows moving point within the text). The 'Remove Special' menu item removes all of these special properties from the text in the region. The invisible and intangible properties are not saved. ## Editing Text-Based Tables The table package provides commands to easily edit text-based tables. Here is an example of what such a table looks like: +-----------------+--------------------------------+-----------------+ | Command | Description | Key Binding | +-----------------+--------------------------------+-----------------+ | forward-char |Move point right N characters | C-f | | |(left if N is negative). | | | | | | +-----------------+--------------------------------+-----------------+ | backward-char |Move point left N characters | C-b | | |(right if N is negative). | | | | | | +-----------------+--------------------------------+-----------------+  When Emacs recognizes such a stretch of text as a table (see Table Recognition), editing the contents of each table cell will automatically resize the table, whenever the contents become too large to fit in the cell. You can use the commands defined in the following sections for navigating and editing the table layout. Type M-x table-fixed-width-mode to toggle the automatic table resizing feature. ## What Is a Text-Based Table? A table consists of a rectangular text area that is divided into cells. Each cell must be at least one character wide and one character high, not counting its border lines. A cell can be subdivided into more cells, but they cannot overlap. Cell border lines are drawn with three special characters, specified by the following variables:  table-cell-vertical-char The character used for vertical lines. The default is '|'. table-cell-horizontal-chars The characters used for horizontal lines. The default is '"-="'. table-cell-intersection-char The character used for the intersection of horizontal and vertical lines. The default is '+'. The following are examples of invalid tables:  +-----+ +--+ +-++--+ | | | | | || | | | | | | || | +--+ | +--+--+ +-++--+ | | | | | | +-++--+ | | | | | | | || | +--+--+ +--+--+ +-++--+ 1 2 3  From left to right: 1. Overlapped cells or non-rectangular cells are not allowed. 2. The border must be rectangular. 3. Cells must have a minimum width/height of one character. ## Creating a Table To create a text-based table from scratch, type M-x table-insert. This command prompts for the number of table columns, the number of table rows, cell width and cell height. The cell width and cell height do not include the cell borders; each can be specified as a single integer (which means each cell is given the same width/height), or as a sequence of integers separated by spaces or commas (which specify the width/height of the individual table columns/rows, counting from left to right for table columns and from top to bottom for table rows). The specified table is then inserted at point. The table inserted by M-x table-insert contains special text properties, which tell Emacs to treat it specially as a text-based table. If you save the buffer to a file and visit it again later, those properties are lost, and the table appears to Emacs as an ordinary piece of text. See the next section, for how to convert it back into a table. ## Table Recognition Existing text-based tables in a buffer, which lack the special text properties applied by M-x table-insert, are not treated specially as tables. To apply those text properties, type M-x table-recognize. This command scans the current buffer, recognizes valid table cells, and applies the relevant text properties. Conversely, type M-x table-unrecognize to unrecognize all tables in the current buffer, removing the special text properties and converting tables back to plain text. You can also use the following commands to selectively recognize or unrecognize tables:  M-x table-recognize-region Recognize tables within the current region. M-x table-unrecognize-region Unrecognize tables within the current region. M-x table-recognize-table Recognize the table at point and activate it. M-x table-unrecognize-table Deactivate the table at point. M-x table-recognize-cell Recognize the cell at point and activate it. M-x table-unrecognize-cell Deactivate the cell at point. See Table Conversion, for another way to recognize a table. ## Commands for Table Cells The commands M-x table-forward-cell and M-x table-backward-cell move point from the current cell to an adjacent cell. The order is cyclic: when point is in the last cell of a table, M-x table-forward-cell moves to the first cell. Likewise, when point is on the first cell, M-x table-backward-cell moves to the last cell. M-x table-span-cell prompts for a direction: right, left, above, or below, and merges the current cell with the adjacent cell in that direction. This command signals an error if the merge would result in an illegitimate cell layout. M-x table-split-cell splits the current cell vertically or horizontally, prompting for the direction with the minibuffer. To split in a specific direction, use M-x table-split-cell-vertically and M-x table-split-cell-horizontally. When splitting vertically, the old cell contents are automatically split between the two new cells. When splitting horizontally, you are prompted for how to divide the cell contents, if the cell is non-empty; the options are 'split' (divide the contents at point), 'left' (put all the contents in the left cell), and 'right' (put all the contents in the right cell). The following commands enlarge or shrink a cell. By default, they resize by one row or column; if a numeric argument is supplied, that specifies the number of rows or columns to resize by.  M-x table-heighten-cell Enlarge the current cell vertically. M-x table-shorten-cell Shrink the current cell vertically. M-x table-widen-cell Enlarge the current cell horizontally. M-x table-narrow-cell Shrink the current cell horizontally. ## Cell Justification The command M-x table-justify imposes justification on one or more cells in a text-based table. Justification determines how the text in the cell is aligned, relative to the edges of the cell. Each cell in a table can be separately justified. M-x table-justify first prompts for what to justify; the options are 'cell' (just the current cell), 'column' (all cells in the current table column) and 'row' (all cells in the current table row). The command then prompts for the justification style; the options are left, center, right, top, middle, bottom, or none (meaning no vertical justification). Horizontal and vertical justification styles are specified independently, and both types can be in effect simultaneously; for instance, you can call M-x table-justify twice, once to specify right justification and once to specify bottom justification, to align the contents of a cell to the bottom right. The justification style is stored in the buffer as a text property, and is lost when you kill the buffer or exit Emacs. However, the table recognition commands, such as M-x table-recognize (see Table Recognition), attempt to determine and re-apply each cell's justification style, by examining its contents. To disable this feature, change the variable table-detect-cell-alignment to nil. ## Table Rows and Columns M-x table-insert-row inserts a row of cells before the current table row. The current row, together with point, is pushed down past the new row. To insert a row after the last row at the bottom of a table, invoke this command with point below the table, just below the bottom edge. You can insert more than one row at a time by using a numeric prefix argument. Similarly, M-x table-insert-column inserts a column of cells to the left of the current table column. To insert a column to the right side of the rightmost column, invoke this command with point to the right of the rightmost column, outside the table. A numeric prefix argument specifies the number of columns to insert. M-x table-delete-column deletes the column of cells at point. Similarly, M-x table-delete-row deletes the row of cells at point. A numeric prefix argument to either command specifies the number of columns or rows to delete. ## Converting Between Plain Text and Tables The command M-x table-capture captures plain text in a region and turns it into a table. Unlike M-x table-recognize (see Table Recognition), the original text does not need to have a table appearance; it only needs to have a logical table-like structure. For example, suppose we have the following numbers, which are divided into three lines and separated horizontally by commas: 1, 2, 3, 4 5, 6, 7, 8 , 9, 10 Invoking M-x table-capture on that text produces this table:  +-----+-----+-----+-----+ |1 |2 |3 |4 | +-----+-----+-----+-----+ |5 |6 |7 |8 | +-----+-----+-----+-----+ | |9 |10 | | +-----+-----+-----+-----+  M-x table-release does the opposite: it converts a table back to plain text, removing its cell borders. One application of this pair of commands is to edit a text in layout. Look at the following three paragraphs (the latter two are indented with header lines): table-capture is a powerful command. Here are some things it can do: Parse Cell Items Using row and column delimiter regexps, it parses the specified text area and extracts cell items into a table.  Applying table-capture to a region containing the above text, with empty strings for the column and row delimiter regexps, creates a table with a single cell like the following one.  +----------------------------------------------------------+ |table-capture is a powerful command. | |Here are some things it can do: | | | |Parse Cell Items Using row and column delimiter regexps,| | it parses the specified text area and | | extracts cell items into a table. | +----------------------------------------------------------+  We can then use the cell splitting commands (see Cell Commands) to subdivide the table so that each paragraph occupies a cell:  +----------------------------------------------------------+ |table-capture is a powerful command. | |Here are some things it can do: | +-----------------+----------------------------------------+ |Parse Cell Items | Using row and column delimiter regexps,| | | it parses the specified text area and | | | extracts cell items into a table. | +-----------------+----------------------------------------+  Each cell can now be edited independently without affecting the layout of other cells. When finished, we can invoke M-x table-release to convert the table back to plain text. ## Table Miscellany The command table-query-dimension reports the layout of the table and table cell at point. Here is an example of its output: Cell: (21w, 6h), Table: (67w, 16h), Dim: (2c, 3r), Total Cells: 5  This indicates that the current cell is 21 characters wide and 6 lines high, the table is 67 characters wide and 16 lines high with 2 columns and 3 rows, and a total of 5 cells. M-x table-insert-sequence inserts a string into each cell. Each string is a part of a sequence i.e., a series of increasing integer numbers. M-x table-generate-source generates a table formatted for a specific markup language. It asks for a language (which must be one of html, latex, or cals), a destination buffer in which to put the result, and a table caption, and then inserts the generated table into the specified buffer. The default destination buffer is table.lang, where lang is the language you specified. ## Two-Column Editing Two-column mode lets you conveniently edit two side-by-side columns of text. It uses two side-by-side windows, each showing its own buffer. There are three ways to enter two-column mode:  2 or C-x 6 2 Enter two-column mode with the current buffer on the left, and on the right, a buffer whose name is based on the current buffer's name (2C-two-columns). If the right buffer doesn't already exist, it starts out empty; the current buffer's contents are not changed. This command is appropriate when the current buffer is empty or contains just one column and you want to add another column. s or C-x 6 s Split the current buffer, which contains two-column text, into two buffers, and display them side by side (2C-split). The current buffer becomes the left buffer, but the text in the right column is moved into the right buffer. The current column specifies the split point. Splitting starts with the current line and continues to the end of the buffer. This command is appropriate when you have a buffer that already contains two-column text, and you wish to separate the columns temporarily. b buffer , C-x 6 b buffer Enter two-column mode using the current buffer as the left buffer, and using buffer buffer as the right buffer (2C-associate-buffer). <F2> s or C-x 6 s looks for a column separator, which is a string that appears on each line between the two columns. You can specify the width of the separator with a numeric argument to <F2> s; that many characters, before point, constitute the separator string. By default, the width is 1, so the column separator is the character before point. When a line has the separator at the proper place, <F2> s puts the text after the separator into the right buffer, and deletes the separator. Lines that don't have the column separator at the proper place remain unsplit; they stay in the left buffer, and the right buffer gets an empty line to correspond. (This is the way to write a line that "spans both columns while in two-column mode": write it in the left buffer, and put an empty line in the right buffer.) The command C-x 6 <RET> or <F2> <RET> (2C-newline) inserts a newline in each of the two buffers at corresponding positions. This is the easiest way to add a new line to the two-column text while editing it in split buffers. When you have edited both buffers as you wish, merge them with <F2> 1 or C-x 6 1 (2C-merge). This copies the text from the right buffer as a second column in the other buffer. To go back to two-column editing, use <F2> s. Use <F2> d or C-x 6 d to dissociate the two buffers, leaving each as it stands (2C-dissociate). If the other buffer, the one not current when you type <F2> d, is empty, <F2> d kills it. ## Editing Programs This chapter describes Emacs features for facilitating editing programs. Some of the things these features can do are: • Find or move over top-level definitions (see Defuns). • Apply the usual indentation conventions of the language (see Program Indent). • Balance parentheses (see Parentheses). • Insert, kill or align comments (see Comments). • Highlight program syntax (see Font Lock). Quick Links: • Program Modes: Major modes for editing programs. • Defuns: Commands to operate on major top-level parts of a program. • Program Indent: Adjusting indentation to show the nesting. • Parentheses: Commands that operate on parentheses. • Comments: Inserting, killing, and aligning comments. • Documentation: Getting documentation of functions you plan to call. • Hideshow: Displaying blocks selectively. • Symbol Completion: Completion on symbol names of your program or language. • Glasses: Making identifiersLikeThis more readable. • Semantic: Suite of editing tools based on source code parsing. • Misc for Programs: Other Emacs features useful for editing programs. • C Modes: Special commands of C, C++, Objective-C, Java, IDL, Pike and AWK modes. • Asm Mode: Asm mode and its special features. • Fortran: Fortran mode and its special features. ## Major Modes for Programming Languages Emacs has specialized major modes (see Major Modes) for many programming languages. A programming language mode typically specifies the syntax of expressions, the customary rules for indentation, how to do syntax highlighting for the language, and how to find the beginning or end of a function definition. It often has features for compiling and debugging programs as well. The major mode for each language is named after the language; for instance, the major mode for the C programming language is c-mode. Emacs has programming language modes for Lisp, Scheme, the Scheme-based DSSSL expression language, Ada, ASM, AWK, C, C++, Delphi, Fortran, Icon, IDL (CORBA), IDLWAVE, Java, JavaScript, Metafont (TeX's companion for font creation), Modula2, Objective-C, Octave, Pascal, Perl, Pike, PostScript, Prolog, Python, Ruby, Simula, Tcl, and VHDL. An alternative mode for Perl is called CPerl mode. Modes are also available for the scripting languages of the common GNU and Unix shells, VMS DCL, and MS-DOS/MS Windows 'BAT' files, and for makefiles, DNS master files, and various sorts of configuration files. Ideally, Emacs should have a major mode for each programming language that you might want to edit. If it doesn't have a mode for your favorite language, the mode might be implemented in a package not distributed with Emacs (see Packages); or you can contribute one. In most programming languages, indentation should vary from line to line to illustrate the structure of the program. Therefore, in most programming language modes, typing <TAB> updates the indentation of the current line (see Program Indent). Furthermore, <DEL> is usually bound to backward-delete-char-untabify, which deletes backward treating each tab as if it were the equivalent number of spaces, so that you can delete one column of indentation without worrying whether the whitespace consists of spaces or tabs. Entering a programming language mode runs the custom Lisp functions specified in the hook variable prog-mode-hook, followed by those specified in the mode's own mode hook (see Major Modes). For instance, entering C mode runs the hooks prog-mode-hook and c-mode-hook. See Hooks, for information about hooks. The Emacs distribution contains Info manuals for the major modes for Ada, C/C++/Objective C/Java/Corba IDL/Pike/AWK, and IDLWAVE. ## Top-Level Definitions, or Defuns In Emacs, a major definition at the top level in the buffer, such as a function, is called a defun. The name comes from Lisp, but in Emacs we use it for all languages. • Left Margin Paren: An open-paren or similar opening delimiter starts a defun if it is at the left margin. • Moving by Defuns: Commands to move over or mark a major definition. • Imenu: Making buffer indexes as menus. • Which Function: Which Function mode shows which function you are in. ## Left Margin Convention Many programming-language modes assume by default that any opening delimiter found at the left margin is the start of a top-level definition, or defun. Therefore, don't put an opening delimiter at the left margin unless it should have that significance. For instance, never put an open-parenthesis at the left margin in a Lisp file unless it is the start of a top-level list. The convention speeds up many Emacs operations, which would otherwise have to scan back to the beginning of the buffer to analyze the syntax of the code. If you don't follow this convention, not only will you have trouble when you explicitly use the commands for motion by defuns; other features that use them will also give you trouble. This includes the indentation commands (see Program Indent) and Font Lock mode (see Font Lock). The most likely problem case is when you want an opening delimiter at the start of a line inside a string. To avoid trouble, put an escape character ('\', in C and Emacs Lisp, '/' in some other Lisp dialects) before the opening delimiter. This will not affect the contents of the string, but will prevent that opening delimiter from starting a defun. Here's an example: (insert "Foo: bar) ")  To help you catch violations of this convention, Font Lock mode highlights confusing opening delimiters (those that ought to be quoted) in bold red. If you need to override this convention, you can do so by setting the variable open-paren-in-column-0-is-defun-start. If this user option is set to t (the default), opening parentheses or braces at column zero always start defuns. When it is nil, defuns are found by searching for parens or braces at the outermost level. Usually, you should leave this option at its default value of t. If your buffer contains parentheses or braces in column zero which don't start defuns, and it is somehow impractical to remove these parentheses or braces, it might be helpful to set the option to nil. Be aware that this might make scrolling and display in large buffers quite sluggish. Furthermore, the parentheses and braces must be correctly matched throughout the buffer for it to work properly. ## Moving By Defuns These commands move point or set up the region based on top-level major definitions, also called defuns.  C-M-a Move to beginning of current or preceding defun (beginning-of-defun). C-M-e Move to end of current or following defun (end-of-defun). C-M-h Put region around whole current or following defun (mark-defun). The commands to move to the beginning and end of the current defun are C-M-a (beginning-of-defun) and C-M-e (end-of-defun). If you repeat one of these commands, or use a positive numeric argument, each repetition moves to the next defun in the direction of motion. C-M-a with a negative argument −n moves forward n times to the next beginning of a defun. This is not exactly the same place that C-M-e with argument n would move to; the end of this defun is not usually exactly the same place as the beginning of the following defun. (Whitespace, comments, and perhaps declarations can separate them.) Likewise, C-M-e with a negative argument moves back to an end of a defun, which is not quite the same as C-M-a with a positive argument. To operate on the current defun, use C-M-h (mark-defun), which sets the mark at the end of the current defun and puts point at its beginning. See Marking Objects. This is the easiest way to get ready to kill the defun order to move it to a different place in the file. If you use the command while point is between defuns, it uses the following defun. If you use the command while the mark is already active, it sets the mark but does not move point; furthermore, each successive use of C-M-h extends the end of the region to include one more defun. In C mode, C-M-h runs the function c-mark-function, which is almost the same as mark-defun; the difference is that it backs up over the argument declarations, function name and returned data type so that the entire C function is inside the region. This is an example of how major modes adjust the standard key bindings so that they do their standard jobs in a way better fitting a particular language. Other major modes may replace any or all of these key bindings for that purpose. ## Imenu The Imenu facility offers a way to find the major definitions in a file by name. It is also useful in text formatter major modes, where it treats each chapter, section, etc., as a definition. (See Tags, for a more powerful feature that handles multiple files together.) If you type M-x imenu, it reads the name of a definition using the minibuffer, then moves point to that definition. You can use completion to specify the name; the command always displays the whole list of valid names. Alternatively, you can bind the command imenu to a mouse click. Then it displays mouse menus for you to select a definition name. You can also add the buffer's index to the menu bar by calling imenu-add-menubar-index. If you want to have this menu bar item available for all buffers in a certain major mode, you can do this by adding imenu-add-menubar-index to its mode hook. But if you have done that, you will have to wait a little while each time you visit a file in that mode, while Emacs finds all the definitions in that buffer. When you change the contents of a buffer, if you add or delete definitions, you can update the buffer's index based on the new contents by invoking the '*Rescan*' item in the menu. Rescanning happens automatically if you set imenu-auto-rescan to a non-nil value. There is no need to rescan because of small changes in the text. You can customize the way the menus are sorted by setting the variable imenu-sort-function. By default, names are ordered as they occur in the buffer; if you want alphabetic sorting, use the symbol imenu--sort-by-name as the value. You can also define a comparison function by writing Lisp code. Imenu provides the information to guide Which Function mode (see Which Function). The Speedbar can also use it (see Speedbar). ## Which Function Mode Which Function mode is a global minor mode (see Minor Modes) which displays the current function name in the mode line, updating it as you move around in a buffer. To either enable or disable Which Function mode, use the command M-x which-function-mode. Which Function mode is a global minor mode. By default, it takes effect in all major modes major modes that know how to support it (i.e., all the major modes that support Imenu). You can restrict it to a specific list of major modes by changing the value of the variable which-func-modes from t (which means to support all available major modes) to a list of major mode names. ## Indentation for Programs The best way to keep a program properly indented is to use Emacs to reindent it as you change it. Emacs has commands to indent either a single line, a specified number of lines, or all of the lines inside a single parenthetical grouping. See Indentation, for general information about indentation. This section describes indentation features specific to programming language modes. Emacs also provides a Lisp pretty-printer in the pp package, which reformats Lisp objects with nice-looking indentation. ## Basic Program Indentation Commands  Adjust indentation of current line (indent-for-tab-command). C-j Insert a newline, then adjust indentation of following line (newline-and-indent). The basic indentation command is <TAB> (indent-for-tab-command), which was documented in Indentation. In programming language modes, <TAB> indents the current line, based on the indentation and syntactic content of the preceding lines; if the region is active, <TAB> indents each line within the region, not just the current line. The command C-j (newline-and-indent), which was documented in Indentation Commands, does the same as <RET> followed by <TAB>: it inserts a new line, then adjusts the line's indentation. When indenting a line that starts within a parenthetical grouping, Emacs usually places the start of the line under the preceding line within the group, or under the text after the parenthesis. If you manually give one of these lines a nonstandard indentation (e.g., for aesthetic purposes), the lines below will follow it. The indentation commands for most programming language modes assume that a open-parenthesis, open-brace or other opening delimiter at the left margin is the start of a function. If the code you are editing violates this assumption—even if the delimiters occur in strings or comments—you must set open-paren-in-column-0-is-defun-start to nil for indentation to work properly. See Left Margin Paren. ## Indenting Several Lines Sometimes, you may want to reindent several lines of code at a time. One way to do this is to use the mark; when the mark is active and the region is non-empty, <TAB> indents every line in the region. Alternatively, the command C-M-\ (indent-region) indents every line in the region, whether or not the mark is active (see Indentation Commands). Also, Emacs provides the following commands for indenting large chunks of code:  C-M-q Reindent all the lines within one parenthetical grouping. C-u Shift an entire parenthetical grouping rigidly sideways so that its first line is properly indented. M-x indent-code-rigidly Shift all the lines in the region rigidly sideways, but do not alter lines that start inside comments and strings. To reindent the contents of a single parenthetical grouping, position point before the beginning of the grouping and type C-M-q. This changes the relative indentation within the grouping, without affecting its overall indentation (i.e., the indentation of the line where the grouping starts). The function that C-M-q runs depends on the major mode; it is indent-pp-sexp in Lisp mode, c-indent-exp in C mode, etc. To correct the overall indentation as well, type <TAB> first. If you like the relative indentation within a grouping but not the indentation of its first line, move point to that first line and type C-u <TAB>. In Lisp, C, and some other major modes, <TAB> with a numeric argument reindents the current line as usual, then reindents by the same amount all the lines in the parenthetical grouping starting on the current line. It is clever, though, and does not alter lines that start inside strings. Neither does it alter C preprocessor lines when in C mode, but it does reindent any continuation lines that may be attached to them. The command M-x indent-code-rigidly rigidly shifts all the lines in the region sideways, like indent-rigidly does (see Indentation Commands). It doesn't alter the indentation of lines that start inside a string, unless the region also starts inside that string. The prefix arg specifies the number of columns to indent. ## Customizing Lisp Indentation The indentation pattern for a Lisp expression can depend on the function called by the expression. For each Lisp function, you can choose among several predefined patterns of indentation, or define an arbitrary one with a Lisp program. The standard pattern of indentation is as follows: the second line of the expression is indented under the first argument, if that is on the same line as the beginning of the expression; otherwise, the second line is indented underneath the function name. Each following line is indented under the previous line whose nesting depth is the same. If the variable lisp-indent-offset is non-nil, it overrides the usual indentation pattern for the second line of an expression, so that such lines are always indented lisp-indent-offset more columns than the containing list. Certain functions override the standard pattern. Functions whose names start with def treat the second lines as the start of a body, by indenting the second line lisp-body-indent additional columns beyond the open-parenthesis that starts the expression. You can override the standard pattern in various ways for individual functions, according to the lisp-indent-function property of the function name. This is normally done for macro definitions, using the declare construct. ## Commands for C Indentation Here are special features for indentation in C mode and related modes:  C-c C-q Reindent the current top-level function definition or aggregate type declaration (c-indent-defun). C-M-q Reindent each line in the balanced expression that follows point (c-indent-exp). A prefix argument inhibits warning messages about invalid syntax. Reindent the current line, and/or in some cases insert a tab character (c-indent-command). If c-tab-always-indent is t, this command always reindents the current line and does nothing else. This is the default. If that variable is nil, this command reindents the current line only if point is at the left margin or in the line's indentation; otherwise, it inserts a tab (or the equivalent number of spaces, if indent-tabs-mode is nil). Any other value (not nil or t) means always reindent the line, and also insert a tab if within a comment or a string. To reindent the whole current buffer, type C-x h C-M-\. This first selects the whole buffer as the region, then reindents that region. To reindent the current block, use C-M-u C-M-q. This moves to the front of the block and then reindents it all. ## Customizing C Indentation C mode and related modes use a flexible mechanism for customizing indentation. C mode indents a source line in two steps: first it classifies the line syntactically according to its contents and context; second, it determines the indentation offset associated by your selected style with the syntactic construct and adds this onto the indentation of the anchor statement.  C-c . style Select a predefined style style (c-set-style). A style is a named collection of customizations that can be used in C mode and the related modes. Styles, for a complete description. Emacs comes with several predefined styles, including gnu, k&r, bsd, stroustrup, linux, python, java, whitesmith, ellemtel, and awk. Some of these styles are primarily intended for one language, but any of them can be used with any of the languages supported by these modes. To find out what a style looks like, select it and reindent some code, e.g., by typing <C-M-q> at the start of a function definition. To choose a style for the current buffer, use the command C-c .. Specify a style name as an argument (case is not significant). This command affects the current buffer only, and it affects only future invocations of the indentation commands; it does not reindent the code already in the buffer. To reindent the whole buffer in the new style, you can type C-x h C-M-\. You can also set the variable c-default-style to specify the default style for various major modes. Its value should be either the style's name (a string) or an alist, in which each element specifies one major mode and which indentation style to use for it. For example, (setq c-default-style '((java-mode . "java") (awk-mode . "awk") (other . "gnu")))  specifies explicit choices for Java and AWK modes, and the default 'gnu' style for the other C-like modes. (These settings are actually the defaults.) This variable takes effect when you select one of the C-like major modes; thus, if you specify a new default style for Java mode, you can make it take effect in an existing Java mode buffer by typing M-x java-mode there. The gnu style specifies the formatting recommended by the GNU Project for C; it is the default, so as to encourage use of our recommended style. As an alternative to specifying a style, you can tell Emacs to guess a style by typing M-x c-guess in a sample code buffer. You can then apply the guessed style to other buffers with M-x c-guess-install. ## Commands For Editing With Parentheses This section describes the commands and features that take advantage of the parenthesis structure in a program, or help you keep it balanced. When talking about these facilities, the term "parenthesis" also includes braces, brackets, or whatever delimiters are defined to match in pairs. The major mode controls which delimiters are significant, through the syntax table. In Lisp, only parentheses count; in C, these commands apply to braces and brackets too. You can use M-x check-parens to find any unbalanced parentheses and unbalanced string quotes in the buffer. • Expressions: Expressions with balanced parentheses. • Moving by Parens: Commands for moving up, down and across in the structure of parentheses. • Matching: Insertion of a close-delimiter flashes matching open. ## Expressions With Balanced Parentheses Each programming language mode has its own definition of a balanced expression. Balanced expressions typically include individual symbols, numbers, and string constants, as well as pieces of code enclosed in a matching pair of delimiters. The following commands deal with balanced expressions (in Emacs, such expressions are referred to internally as sexps10).  C-M-f Move forward over a balanced expression (forward-sexp). C-M-b Move backward over a balanced expression (backward-sexp). C-M-k Kill balanced expression forward (kill-sexp). C-M-t Transpose expressions (transpose-sexps). [email protected], C-M- Put mark after following expression (mark-sexp). To move forward over a balanced expression, use C-M-f (forward-sexp). If the first significant character after point is an opening delimiter (e.g., '(', '[' or '{' in C), this command moves past the matching closing delimiter. If the character begins a symbol, string, or number, the command moves over that. The command C-M-b (backward-sexp) moves backward over a balanced expression—like C-M-f, but in the reverse direction. If the expression is preceded by any prefix characters (single-quote, backquote and comma, in Lisp), the command moves back over them as well. C-M-f or C-M-b with an argument repeats that operation the specified number of times; with a negative argument means to move in the opposite direction. In most modes, these two commands move across comments as if they were whitespace. Note that their keys, C-M-f and C-M-b, are analogous to C-f and C-b, which move by characters (see Moving Point), and M-f and M-b, which move by words (see Words). To kill a whole balanced expression, type C-M-k (kill-sexp). This kills the text that C-M-f would move over. C-M-t (transpose-sexps) switches the positions of the previous balanced expression and the next one. It is analogous to the C-t command, which transposes characters (see Transpose). An argument to C-M-t serves as a repeat count, moving the previous expression over that many following ones. A negative argument moves the previous balanced expression backwards across those before it. An argument of zero, rather than doing nothing, transposes the balanced expressions ending at or after point and the mark. To operate on balanced expressions with a command which acts on the region, type C-M-<SPC> (mark-sexp). This sets the mark where C-M-f would move to. While the mark is active, each successive call to this command extends the region by shifting the mark by one expression. Positive or negative numeric arguments move the mark forward or backward by the specified number of expressions. The alias [email protected] is equivalent to C-M-<SPC>. See Marking Objects, for more information about this and related commands. In languages that use infix operators, such as C, it is not possible to recognize all balanced expressions because there can be multiple possibilities at a given position. For example, C mode does not treat 'foo + bar' as a single expression, even though it is one C expression; instead, it recognizes 'foo' as one expression and 'bar' as another, with the '+' as punctuation between them. However, C mode recognizes '(foo + bar)' as a single expression, because of the parentheses. ## Moving in the Parenthesis Structure The following commands move over groupings delimited by parentheses (or whatever else serves as delimiters in the language you are working with). They ignore strings and comments, including any parentheses within them, and also ignore parentheses that are "quoted" with an escape character. These commands are mainly intended for editing programs, but can be useful for editing any text containing parentheses. They are referred to internally as "list" commands because in Lisp these groupings are lists. These commands assume that the starting point is not inside a string or a comment. If you invoke them from inside a string or comment, the results are unreliable.  C-M-n Move forward over a parenthetical group (forward-list). C-M-p Move backward over a parenthetical group (backward-list). C-M-u Move up in parenthesis structure (backward-up-list). C-M-d Move down in parenthesis structure (down-list). The "list" commands C-M-n (forward-list) and C-M-p (backward-list) move forward or backward over one (or n) parenthetical groupings. C-M-n and C-M-p try to stay at the same level in the parenthesis structure. To move up one (or n) levels, use C-M-u (backward-up-list). C-M-u moves backward up past one unmatched opening delimiter. A positive argument serves as a repeat count; a negative argument reverses the direction of motion, so that the command moves forward and up one or more levels. To move down in the parenthesis structure, use C-M-d (down-list). In Lisp mode, where '(' is the only opening delimiter, this is nearly the same as searching for a '('. An argument specifies the number of levels to go down. ## Matching Parentheses Emacs has a number of parenthesis matching features, which make it easy to see how and whether parentheses (or other delimiters) match up. Whenever you type a self-inserting character that is a closing delimiter, the cursor moves momentarily to the location of the matching opening delimiter, provided that is on the screen. If it is not on the screen, Emacs displays some of the text near it in the echo area. Either way, you can tell which grouping you are closing off. If the opening delimiter and closing delimiter are mismatched—such as in '[x)'—a warning message is displayed in the echo area. Three variables control the display of matching parentheses: • blink-matching-paren turns the feature on or off: nil disables it, but the default is t to enable it. • blink-matching-delay says how many seconds to leave the cursor on the matching opening delimiter, before bringing it back to the real location of point. This may be an integer or floating-point number; the default is 1. • blink-matching-paren-distance specifies how many characters back to search to find the matching opening delimiter. If the match is not found in that distance, Emacs stops scanning and nothing is displayed. The default is 102400. Show Paren mode, a global minor mode, provides a more powerful kind of automatic matching. Whenever point is before an opening delimiter or after a closing delimiter, both that delimiter and its opposite delimiter are highlighted. To toggle Show Paren mode, type M-x show-paren-mode. Electric Pair mode, a global minor mode, provides a way to easily insert matching delimiters. Whenever you insert an opening delimiter, the matching closing delimiter is automatically inserted as well, leaving point between the two. To toggle Electric Pair mode, type M-x electric-pair-mode. ## Manipulating Comments Because comments are such an important part of programming, Emacs provides special commands for editing and inserting comments. It can also do spell checking on comments with Flyspell Prog mode (see Spelling). Some major modes have special rules for indenting different kinds of comments. For example, in Lisp code, comments starting with two semicolons are indented as if they were lines of code, while those starting with three semicolons are supposed to be aligned to the left margin and are often used for sectioning purposes. Emacs understand these conventions; for instance, typing <TAB> on a comment line will indent the comment to the appropriate position. ;; This function is just an example. ;;; Here either two or three semicolons are appropriate. (defun foo (x) ;;; And now, the first part of the function: ;; The following line adds one. (1+ x)) ; This line adds one. ## Comment Commands The following commands operate on comments:  M-; Insert or realign comment on current line; if the region is active, comment or uncomment the region instead (comment-dwim). C-u M-; Kill comment on current line (comment-kill). C-x ; Set comment column (comment-set-column). C-M-j, M-j Like followed by inserting and aligning a comment (comment-indent-new-line). See Multi-Line Comments. M-x comment-region, C-c C-c (C-c C-c operates in C-like modes.) Add comment delimiters to all the lines in the region. The command to create or align a comment is M-; (comment-dwim). The word "dwim" is an acronym for "Do What I Mean"; it indicates that this command can be used for many different jobs relating to comments, depending on the situation where you use it. When a region is active (see Mark), M-; either adds comment delimiters to the region, or removes them. If every line in the region is already a comment, it "uncomments" each of those lines by removing their comment delimiters. Otherwise, it adds comment delimiters to enclose the text in the region. If you supply a prefix argument to M-; when a region is active, that specifies the number of comment delimiters to add or delete. A positive argument n adds n delimiters, while a negative argument -n removes n delimiters. If the region is not active, and there is no existing comment on the current line, M-; adds a new comment to the current line. If the line is blank (i.e., empty or containing only whitespace characters), the comment is indented to the same position where <TAB> would indent to (see Basic Indent). If the line is non-blank, the comment is placed after the last non-whitespace character on the line; normally, Emacs tries putting it at the column specified by the variable comment-column (see Options for Comments), but if the line already extends past that column, it puts the comment at some suitable position, usually separated from the non-comment text by at least one space. In each case, Emacs places point after the comment's starting delimiter, so that you can start typing the comment text right away. You can also use M-; to align an existing comment. If a line already contains the comment-start string, M-; realigns it to the conventional alignment and moves point after the comment's starting delimiter. As an exception, comments starting in column 0 are not moved. Even when an existing comment is properly aligned, M-; is still useful for moving directly to the start of the comment text. C-u M-; (comment-dwim with a prefix argument) kills any comment on the current line, along with the whitespace before it. Since the comment is saved to the kill ring, you can reinsert it on another line by moving to the end of that line, doing C-y, and then M-; to realign the comment. You can achieve the same effect as C-u M-; by typing M-x comment-kill (comment-dwim actually calls comment-kill as a subroutine when it is given a prefix argument). The command M-x comment-region is equivalent to calling M-; on an active region, except that it always acts on the region, even if the mark is inactive. In C mode and related modes, this command is bound to C-c C-c. The command M-x uncomment-region uncomments each line in the region; a numeric prefix argument specifies the number of comment delimiters to remove (negative arguments specify the number of comment to delimiters to add). For C-like modes, you can configure the exact effect of M-; by setting the variables c-indent-comment-alist and c-indent-comments-syntactically-p. For example, on a line ending in a closing brace, M-; puts the comment one space after the brace rather than at comment-column. For full details see Comment Commands. ## Multiple Lines of Comments If you are typing a comment and wish to continue it to another line, type M-j or C-M-j (comment-indent-new-line). This breaks the current line, and inserts the necessary comment delimiters and indentation to continue the comment. For languages with closing comment delimiters (e.g., '*/' in C), the exact behavior of M-j depends on the value of the variable comment-multi-line. If the value is nil, the command closes the comment on the old line and starts a new comment on the new line. Otherwise, it opens a new line within the current comment delimiters. When Auto Fill mode is on, going past the fill column while typing a comment also continues the comment, in the same way as an explicit invocation of M-j. To turn existing lines into comment lines, use M-; with the region active, or use M-x comment-region as described in the preceding section. You can configure C Mode such that when you type a '/' at the start of a line in a multi-line block comment, this closes the comment. Enable the comment-close-slash clean-up for this. ## Options Controlling Comments As mentioned in Comment Commands, when the M-j command adds a comment to a line, it tries to place the comment at the column specified by the buffer-local variable comment-column. You can set either the local value or the default value of this buffer-local variable in the usual way (see Locals). Alternatively, you can type C-x ; (comment-set-column) to set the value of comment-column in the current buffer to the column where point is currently located. C-u C-x ; sets the comment column to match the last comment before point in the buffer, and then does a M-; to align the current line's comment under the previous one. The comment commands recognize comments based on the regular expression that is the value of the variable comment-start-skip. Make sure this regexp does not match the null string. It may match more than the comment starting delimiter in the strictest sense of the word; for example, in C mode the value of the variable is "\\(//+\\|/\\*+\\\s *", which matches extra stars and spaces after the '/*' itself, and accepts C++ style comments also. (Note that '\\' is needed in Lisp syntax to include a '\' in the string, which is needed to deny the first star its special meaning in regexp syntax. See Regexp Backslash.) When a comment command makes a new comment, it inserts the value of comment-start as an opening comment delimiter. It also inserts the value of comment-end after point, as a closing comment delimiter. For example, in Lisp mode, comment-start is '";"' and comment-end is "" (the empty string). In C mode, comment-start is "/* " and comment-end is " */". The variable comment-padding specifies a string that the commenting commands should insert between the comment delimiter(s) and the comment text. The default, '" "', specifies a single space. Alternatively, the value can be a number, which specifies that number of spaces, or nil, which means no spaces at all. The variable comment-multi-line controls how M-j and Auto Fill mode continue comments over multiple lines. See Multi-Line Comments. The variable comment-indent-function should contain a function that will be called to compute the alignment for a newly inserted comment or for aligning an existing comment. It is set differently by various major modes. The function is called with no arguments, but with point at the beginning of the comment, or at the end of a line if a new comment is to be inserted. It should return the column in which the comment ought to start. For example, in Lisp mode, the indent hook function bases its decision on how many semicolons begin an existing comment, and on the code in the preceding lines. ## Documentation Lookup Emacs provides several features you can use to look up the documentation of functions, variables and commands that you plan to use in your program. • Info Lookup: Looking up library functions and commands in Info files. • Man Page: Looking up man pages of library functions and commands. • Lisp Doc: Looking up Emacs Lisp functions, etc. ## Info Documentation Lookup For major modes that apply to languages which have documentation in Info, you can use C-h S (info-lookup-symbol) to view the Info documentation for a symbol used in the program. You specify the symbol with the minibuffer; the default is the symbol appearing in the buffer at point. For example, in C mode this looks for the symbol in the C Library Manual. The command only works if the appropriate manual's Info files are installed. The major mode determines where to look for documentation for the symbol—which Info files to look in, and which indices to search. You can also use M-x info-lookup-file to look for documentation for a file name. If you use C-h S in a major mode that does not support it, it asks you to specify the "symbol help mode". You should enter a command such as c-mode that would select a major mode which C-h S does support. ## Man Page Lookup On Unix, the main form of on-line documentation was the manual page or man page. In the GNU operating system, we aim to replace man pages with better-organized manuals that you can browse with Info (see Misc Help). This process is not finished, so it is still useful to read manual pages. You can read the man page for an operating system command, library function, or system call, with the M-x man command. This prompts for a topic, with completion (see Completion), and runs the man program to format the corresponding man page. If the system permits, it runs man asynchronously, so that you can keep on editing while the page is being formatted. The result goes in a buffer named *Man topic*. These buffers use a special major mode, Man mode, that facilitates scrolling and jumping to other manual pages. For details, type C-h m while in a Man mode buffer. Each man page belongs to one of ten or more sections, each named by a digit or by a digit and a letter. Sometimes there are man pages with the same name in different sections. To read a man page from a specific section, type 'topic(section)' or 'section topic' when M-x manual-entry prompts for the topic. For example, the man page for the C library function chmod is in section 2, but there is a shell command of the same name, whose man page is in section 1; to view the former, you must specify the chapter number in parentheses. For example: M-x manual-entry <RET> chmod(2) <RET>. If you do not specify a section, M-x man normally displays only the first man page found. On some systems, the man program accepts a '-a' command-line option, which tells it to display all the man pages for the specified topic. To make use of this, change the value of the variable Man-switches to '"-a"'. Then, in the Man mode buffer, you can type M-n and M-p to switch between man pages in different sections. The mode line shows how many manual pages are available. An alternative way of reading manual pages is the M-x woman command. Unlike M-x man, it does not run any external programs to format and display the man pages; the formatting is done by Emacs, so it works on systems such as MS Windows where the man program may be unavailable. It prompts for a man page, and displays it in a buffer named *WoMan section topic. M-x woman computes the completion list for manpages the first time you invoke the command. With a numeric argument, it recomputes this list; this is useful if you add or delete manual pages. If you type a name of a manual page and M-x woman finds that several manual pages by the same name exist in different sections, it pops up a window with possible candidates asking you to choose one of them. For more information about setting up and using M-x woman, see the WoMan Info manual, which is distributed with Emacs. ## Emacs Lisp Documentation Lookup When editing Emacs Lisp code, you can use the commands C-h f (describe-function) and C-h v (describe-variable) to view the built-in documentation for the Lisp functions and variables that you want to use. See Name Help. Eldoc is a buffer-local minor mode that helps with looking up Lisp documention. When it is enabled, the echo area displays some useful information whenever there is a Lisp function or variable at point; for a function, it shows the argument list, and for a variable it shows the first line of the variable's documentation string. To toggle Eldoc mode, type M-x eldoc-mode. Eldoc mode can be used with the Emacs Lisp and Lisp Interaction major modes. ## Hideshow Minor Mode Hideshow mode is a buffer-local minor mode that allows you to selectively display portions of a program, which are referred to as blocks. Type M-x hs-minor-mode to toggle this minor mode (see Minor Modes). When you use Hideshow mode to hide a block, the block disappears from the screen, to be replaced by an ellipsis (three periods in a row). Just what constitutes a block depends on the major mode. In C mode and related modes, blocks are delimited by braces, while in Lisp mode they are delimited by parentheses. Multi-line comments also count as blocks. Hideshow mode provides the following commands:  C-c @ C-h Hide the current block (hs-hide-block). C-c @ C-s Show the current block (hs-show-block). C-c @ C-c Either hide or show the current block (hs-toggle-hiding). S-Mouse-2 Toggle hiding for the block you click on (hs-mouse-toggle-hiding). C-c @ C-M-h Hide all top-level blocks (hs-hide-all). C-c @ C-M-s Show all blocks in the buffer (hs-show-all). C-c @ C-l Hide all blocks n levels below this block (hs-hide-level). These variables can be used to customize Hideshow mode:  hs-hide-comments-when-hiding-all If non-nil, C-c @ C-M-h (hs-hide-all) hides comments too. hs-isearch-open This variable specifies the conditions under which incremental search should unhide a hidden block when matching text occurs within the block. Its value should be either code (unhide only code blocks), comment (unhide only comments), t (unhide both code blocks and comments), or nil (unhide neither code blocks nor comments). The default value is code. ## Completion for Symbol Names Completion is normally done in the minibuffer (see Completion), but you can also complete symbol names in ordinary Emacs buffers. In programming language modes, type C-M-i or M-<TAB> to complete the partial symbol before point. On graphical displays, the M-<TAB> key is usually reserved by the window manager for switching graphical windows, so you should type C-M-i or <ESC> <TAB> instead. In most programming language modes, C-M-i (or M-<TAB>) invokes the command completion-at-point, which generates its completion list in a flexible way. If Semantic mode is enabled, it tries to use the Semantic parser data for completion (see Semantic). If Semantic mode is not enabled or fails at performing completion, it tries to complete using the selected tags table (see Tags). If in Emacs Lisp mode, it performs completion using the function, variable, or property names defined in the current Emacs session. In all other respects, in-buffer symbol completion behaves like minibuffer completion. For instance, if Emacs cannot complete to a unique symbol, it displays a list of completion alternatives in another window. See Completion. In Text mode and related modes, M-<TAB> completes words based on the spell-checker's dictionary. See Spelling. ## Glasses Minor Mode Glasses mode is a buffer-local minor mode that makes it easier to read mixed-case (or "CamelCase") symbols like 'unReadableSymbol', by altering how they are displayed. By default, it displays extra underscores between each lower-case letter and the following capital letter. This does not alter the buffer text, only how it is displayed. To toggle Glasses mode, type M-x glasses-mode (see Minor Modes). When Glasses mode is enabled, the minor mode indicator 'o^o' appears in the mode line. For more information about Glasses mode, type C-h P glasses <RET>. ## Semantic Semantic is a package that provides language-aware editing commands based on source code parsers. Most of the "language aware" features in Emacs, such as Font Lock mode (see Font Lock), rely on "rules of thumb" that usually give good results but are never completely exact. In contrast, the parsers used by Semantic have an exact understanding of programming language syntax. This allows Semantic to provide search, navigation, and completion commands that are powerful and precise. To begin using Semantic, type M-x semantic-mode or click on the menu item named 'Source Code Parsers (Semantic)' in the 'Tools' menu. This enables Semantic mode, a global minor mode. When Semantic mode is enabled, Emacs automatically attempts to parses each file you visit. Currently, Semantic understands C, C++, Scheme, JavaScript, Java, HTML, and Make. Within each parsed buffer, the following commands are available:  C-c , j Prompt for the name of a function defined in the current file, and move point there (semantic-complete-jump-local). C-c , J Prompt for the name of a function defined in any file Emacs has parsed, and move point there (semantic-complete-jump). C-c , Display a list of possible completions for the symbol at point (semantic-complete-analyze-inline). This also activates a set of special key bindings for choosing a completion: accepts the current completion, M-n and M-p cycle through possible completions, completes as far as possible and then cycles, and C-g or any other key aborts completion. C-c , l Display a list of the possible completions of the symbol at point, in another window (semantic-analyze-possible-completions). In addition to the above commands, the Semantic package provides a variety of other ways to make use of parser information. For instance, you can use it to display a list of completions when Emacs is idle. ## Other Features Useful for Editing Programs Some Emacs commands that aren't designed specifically for editing programs are useful for that nonetheless. The Emacs commands that operate on words, sentences and paragraphs are useful for editing code. Most symbols names contain words (see Words), while sentences can be found in strings and comments (see Sentences). As for paragraphs, they are defined in most programming language modes to begin and end at blank lines (see Paragraphs). Therefore, judicious use of blank lines to make the program clearer will also provide useful chunks of text for the paragraph commands to work on. Auto Fill mode, if enabled in a programming language major mode, indents the new lines which it creates. Electric Layout mode (M-x electric-layout-mode) is a global minor mode that automatically inserts newlines when you type certain characters; for example, '{', '}' and ';' in JavaScript mode. Apart from Hideshow mode (see Hideshow), another way to selectively display parts of a program is to use the selective display feature (see Selective Display). Programming modes often also support Outline minor mode (see Outline Mode), which can be used with the Foldout package (see Foldout). ## C and Related Modes This section gives a brief description of the special features available in C, C++, Objective-C, Java, CORBA IDL, Pike and AWK modes. (These are called "C mode and related modes".) For more details, see the CC mode Info manual, which is distributed with Emacs. ## C Mode Motion Commands This section describes commands for moving point, in C mode and related modes.  C-M-a, C-M-e Move point to the beginning or end of the current function or top-level definition. In languages with enclosing scopes (such as C++'s classes) the current function is the immediate one, possibly inside a scope. Otherwise, it is the one defined by the least enclosing braces. (By contrast, beginning-of-defun and end-of-defun search for braces in column zero.) See Moving by Defuns. C-c C-u Move point back to the containing preprocessor conditional, leaving the mark behind. A prefix argument acts as a repeat count. With a negative argument, move point forward to the end of the containing preprocessor conditional. '#elif' is equivalent to '#else' followed by '#if', so the function will stop at a '#elif' when going backward, but not when going forward. C-c C-p Move point back over a preprocessor conditional, leaving the mark behind. A prefix argument acts as a repeat count. With a negative argument, move forward. C-c C-n Move point forward across a preprocessor conditional, leaving the mark behind. A prefix argument acts as a repeat count. With a negative argument, move backward. M-a Move point to the beginning of the innermost C statement (c-beginning-of-statement). If point is already at the beginning of a statement, move to the beginning of the preceding statement. With prefix argument n, move back n − 1 statements. In comments or in strings which span more than one line, this command moves by sentences instead of statements. M-e Move point to the end of the innermost C statement or sentence; like M-a except that it moves in the other direction (c-end-of-statement). ## Electric C Characters In C mode and related modes, certain printing characters are electric—in addition to inserting themselves, they also reindent the current line, and optionally also insert newlines. The "electric" characters are {, }, :, #, ;, ,, <, >, /, *, (, and ). You might find electric indentation inconvenient if you are editing chaotically indented code. If you are new to CC Mode, you might find it disconcerting. You can toggle electric action with the command C-c C-l; when it is enabled, '/l' appears in the mode line after the mode name:  C-c C-l Toggle electric action (c-toggle-electric-state). With a positive prefix argument, this command enables electric action, with a negative one it disables it. Electric characters insert newlines only when, in addition to the electric state, the auto-newline feature is enabled (indicated by '/la' in the mode line after the mode name). You can turn this feature on or off with the command C-c C-a:  C-c C-a Toggle the auto-newline feature (c-toggle-auto-newline). With a prefix argument, this command turns the auto-newline feature on if the argument is positive, and off if it is negative. Usually the CC Mode style configures the exact circumstances in which Emacs inserts auto-newlines. You can also configure this directly. ## Hungry Delete Feature in C If you want to delete an entire block of whitespace at point, you can use hungry deletion. This deletes all the contiguous whitespace either before point or after point in a single operation. Whitespace here includes tabs and newlines, but not comments or preprocessor commands.  C-c C-, C-c Delete the entire block of whitespace preceding point (c-hungry-delete-backwards). C-c C-d, C-c C-, C-c Delete the entire block of whitespace after point (c-hungry-delete-forward). As an alternative to the above commands, you can enable hungry delete mode. When this feature is enabled (indicated by '/h' in the mode line after the mode name), a single <DEL> deletes all preceding whitespace, not just one space, and a single C-c C-d (but not plain <DELETE>) deletes all following whitespace.  M-x c-toggle-hungry-state Toggle the hungry-delete feature (c-toggle-hungry-state). With a prefix argument, this command turns the hungry-delete feature on if the argument is positive, and off if it is negative. The variable c-hungry-delete-key controls whether the hungry-delete feature is enabled. ## Other Commands for C Mode  C-c C-w, M-x subword-mode Enable (or disable) subword mode. In subword mode, Emacs's word commands recognize upper case letters in 'StudlyCapsIdentifiers' as word boundaries. This is indicated by the flag '/w' on the mode line after the mode name (e.g., 'C/law'). You can even use M-x subword-mode in non-CC Mode buffers. In the GNU project, we recommend using underscores to separate words within an identifier in C or C++, rather than using case distinctions. M-x c-context-line-break This command inserts a line break and indents the new line in a manner appropriate to the context. In normal code, it does the work of C-j (newline-and-indent), in a C preprocessor line it additionally inserts a '\' at the line break, and within comments it's like M-j (c-indent-new-comment-line). c-context-line-break isn't bound to a key by default, but it needs a binding to be useful. The following code will bind it to C-j. We use c-initialization-hook here to make sure the keymap is loaded before we try to change it. (defun my-bind-clb () (define-key c-mode-base-map "\C-j" 'c-context-line-break)) (add-hook 'c-initialization-hook 'my-bind-clb)  C-M-h Put mark at the end of a function definition, and put point at the beginning (c-mark-function). M-q Fill a paragraph, handling C and C++ comments (c-fill-paragraph). If any part of the current line is a comment or within a comment, this command fills the comment or the paragraph of it that point is in, preserving the comment indentation and comment delimiters. C-c C-e Run the C preprocessor on the text in the region, and show the result, which includes the expansion of all the macro calls (c-macro-expand). The buffer text before the region is also included in preprocessing, for the sake of macros defined there, but the output from this part isn't shown. When you are debugging C code that uses macros, sometimes it is hard to figure out precisely how the macros expand. With this command, you don't have to figure it out; you can see the expansions. C-c C-\ Insert or align '\' characters at the ends of the lines of the region (c-backslash-region). This is useful after writing or editing a C macro definition. If a line already ends in '\', this command adjusts the amount of whitespace before it. Otherwise, it inserts a new '\'. However, the last line in the region is treated specially; no '\' is inserted on that line, and any '\' there is deleted. M-x cpp-highlight-buffer Highlight parts of the text according to its preprocessor conditionals. This command displays another buffer named *CPP Edit*, which serves as a graphic menu for selecting how to display particular kinds of conditionals and their contents. After changing various settings, click on '[A]pply these settings' (or go to that buffer and type a) to rehighlight the C mode buffer accordingly. C-c C-s Display the syntactic information about the current source line (c-show-syntactic-information). This information directs how the line is indented. M-x cwarn-mode, M-x global-cwarn-mode CWarn minor mode highlights certain suspicious C and C++ constructions: Assignments inside expressions. Semicolon following immediately after 'if', 'for', and 'while' (except after a 'do ... while' statement); C++ functions with reference parameters. You can enable the mode for one buffer with the command M-x cwarn-mode, or for all suitable buffers with the command M-x global-cwarn-mode or by customizing the variable global-cwarn-mode. You must also enable Font Lock mode to make it work. M-x hide-ifdef-mode Hide-ifdef minor mode hides selected code within '#if' and '#ifdef' preprocessor blocks. If you change the variable hide-ifdef-shadow to t, Hide-ifdef minor mode "shadows" preprocessor blocks by displaying them with a less prominent face, instead of hiding them entirely. See the documentation string of hide-ifdef-mode for more information. M-x ff-find-related-file Find a file "related" in a special way to the file visited by the current buffer. Typically this will be the header file corresponding to a C/C++ source file, or vice versa. The variable ff-related-file-alist specifies how to compute related file names. ## Asm Mode Asm mode is a major mode for editing files of assembler code. It defines these commands:  tab-to-tab-stop. C-j Insert a newline and then indent using tab-to-tab-stop. : Insert a colon and then remove the indentation from before the label preceding colon. Then do tab-to-tab-stop. ; Insert or align a comment. The variable asm-comment-char specifies which character starts comments in assembler syntax. ## Fortran Mode Fortran mode is meant for editing "fixed form" (and also "tab format") source code (normally Fortran 77). For editing more modern "free form" source code (Fortran 90, 95, 2003, 2008), use F90 mode (f90-mode). Emacs normally uses Fortran mode for files with extension '.f', '.F' or '.for', and F90 mode for the extensions '.f90', '.f95', '.f03' and '.f08'. Customize auto-mode-alist to add more extensions. GNU Fortran supports both free and fixed form. This manual mainly documents Fortran mode, but the corresponding F90 mode features are mentioned when relevant. Fortran mode provides special motion commands for Fortran statements and subprograms, and indentation commands that understand Fortran conventions of nesting, line numbers and continuation statements. Fortran mode has support for Auto Fill mode that breaks long lines into proper Fortran continuation lines. Fortran mode also supports Hideshow minor mode (see Hideshow), and Imenu (see Imenu). Special commands for comments are provided because Fortran comments are unlike those of other languages. Built-in abbrevs optionally save typing when you insert Fortran keywords. Use M-x fortran-mode to switch to this major mode. This command runs the hook fortran-mode-hook. See Hooks. • Motion: Moving point by statements or subprograms. • Indent: Indentation commands for Fortran. • Comments: Inserting and aligning comments. • Autofill: Auto fill support for Fortran. • Columns: Measuring columns for valid Fortran. • Abbrev: Built-in abbrevs for Fortran keywords. ## Fortran Motion Commands In addition to the normal commands for moving by and operating on "defuns" (Fortran subprograms—functions and subroutines, as well as modules for F90 mode, using the commands fortran-end-of-subprogram and fortran-beginning-of-subprogram), Fortran mode provides special commands to move by statements and other program units.  C-c C-n Move to the beginning of the next statement (fortran-next-statement/f90-next-statement). C-c C-p Move to the beginning of the previous statement (fortran-previous-statement/f90-previous-statement). If there is no previous statement (i.e., if called from the first statement in the buffer), move to the start of the buffer. C-c C-e Move point forward to the start of the next code block, or the end of the current one, whichever comes first (f90-next-block). A code block is a subroutine, if–endif statement, and so forth. This command exists for F90 mode only, not Fortran mode. With a numeric argument, it moves forward that many blocks. C-c C-a Move point backward to the previous block (f90-previous-block). This is like f90-next-block, but moves backwards. C-M-n Move to the end of the current code block (fortran-end-of-block/f90-end-of-block). With a numeric argument, move forward that number of blocks. The mark is set before moving point. The F90 mode version of this command checks for consistency of block types and labels (if present), but it does not check the outermost block since that may be incomplete. C-M-p Move to the start of the current code block (fortran-beginning-of-block/f90-beginning-of-block). This is like fortran-end-of-block, but moves backwards. The commands fortran-beginning-of-subprogram and fortran-end-of-subprogram move to the start or end of the current subprogram, respectively. The commands fortran-mark-do and fortran-mark-if mark the end of the current do or if block, and move point to the start. ## Fortran Indentation Special commands and features are needed for indenting fixed (or tab) form Fortran code to make sure various syntactic entities (line numbers, comment line indicators and continuation line flags) appear in the required columns. • Commands: Commands for indenting and filling Fortran. • Contline: How continuation lines indent. • Numbers: How line numbers auto-indent. • Conv: Conventions you must obey to avoid trouble. • Vars: Variables controlling Fortran indent style. ## Fortran Indentation and Filling Commands  C-M-j Break the current line at point and set up a continuation line (fortran-split-line). M-^ Join this line to the previous line (fortran-join-line). C-M-q Indent all the lines of the subprogram that point is in (fortran-indent-subprogram). M-q Fill a comment block or statement (using fortran-fill-paragraph or fortran-fill-statement). The key C-M-q runs fortran-indent-subprogram, a command to reindent all the lines of the Fortran subprogram (function or subroutine) containing point. The key C-M-j runs fortran-split-line, which splits a line in the appropriate fashion for Fortran. In a non-comment line, the second half becomes a continuation line and is indented accordingly. In a comment line, both halves become separate comment lines. M-^ or C-c C-d runs the command fortran-join-line, which joins a continuation line back to the previous line, roughly as the inverse of fortran-split-line. The point must be on a continuation line when this command is invoked. M-q in Fortran mode fills the comment block or statement that point is in. This removes any excess statement continuations. ## Continuation Lines Most Fortran 77 compilers allow two ways of writing continuation lines. If the first non-space character on a line is in column 5, then that line is a continuation of the previous line. We call this fixed form. (In GNU Emacs we always count columns from 0; but note that the Fortran standard counts from 1.) The variable fortran-continuation-string specifies what character to put in column 5. A line that starts with a tab character followed by any digit except '0' is also a continuation line. We call this style of continuation tab format. (Fortran 90 introduced "free form", with another style of continuation lines). Fortran mode can use either style of continuation line. When you enter Fortran mode, it tries to deduce the proper continuation style automatically from the buffer contents. It does this by scanning up to fortran-analyze-depth (default 100) lines from the start of the buffer. The first line that begins with either a tab character or six spaces determines the choice. If the scan fails (for example, if the buffer is new and therefore empty), the value of fortran-tab-mode-default (nil for fixed form, and non-nil for tab format) is used. '/t' (fortran-tab-mode-string) in the mode line indicates tab format is selected. Fortran mode sets the value of indent-tabs-mode accordingly. If the text on a line starts with the Fortran continuation marker '', or if it begins with any non-whitespace character in column 5, Fortran mode treats it as a continuation line. When you indent a continuation line with <TAB>, it converts the line to the current continuation style. When you split a Fortran statement with C-M-j, the continuation marker on the newline is created according to the continuation style.

The setting of continuation style affects other aspects of editing in Fortran mode. In fixed form mode, the minimum column number for the body of a statement is 6. Lines inside of Fortran blocks that are indented to larger column numbers must use only the space character for whitespace. In tab format mode, the minimum column number for the statement body is 8, and the whitespace before column 8 must consist of one tab character.

## Fortran Line Numbers

If a number is the first non-whitespace in the line, Fortran indentation assumes it is a line number and moves it to columns 0 through 4. (Columns always count from 0 in Emacs.)

Line numbers of four digits or less are normally indented one space. The variable fortran-line-number-indent controls this; it specifies the maximum indentation a line number can have. The default value of the variable is 1. Fortran mode tries to prevent line number digits passing column 4, reducing the indentation below the specified maximum if necessary. If fortran-line-number-indent has the value 5, line numbers are right-justified to end in column 4.

Inserting a line number is enough to indent it according to these rules. As each digit is inserted, the indentation is recomputed. To turn off this feature, set the variable fortran-electric-line-number to nil.

## Syntactic Conventions

Fortran mode assumes that you follow certain conventions that simplify the task of understanding a Fortran program well enough to indent it properly:

• Two nested 'do' loops never share a 'continue' statement.
• Fortran keywords such as 'if', 'else', 'then', 'do' and others are written without embedded whitespace or line breaks.
• Fortran compilers generally ignore whitespace outside of string constants, but Fortran mode does not recognize these keywords if they are not contiguous. Constructs such as 'else if' or 'end do' are acceptable, but the second word should be on the same line as the first and not on a continuation line.

If you fail to follow these conventions, the indentation commands may indent some lines unaesthetically. However, a correct Fortran program retains its meaning when reindented even if the conventions are not followed.

## Variables for Fortran Indentation

Several additional variables control how Fortran indentation works:

 fortran-do-indent Extra indentation within each level of 'do' statement (default 3). fortran-if-indent Extra indentation within each level of 'if', 'select case', or 'where' statements (default 3). fortran-structure-indent Extra indentation within each level of 'structure', 'union', 'map', or 'interface' statements (default 3). fortran-continuation-indent Extra indentation for bodies of continuation lines (default 5). fortran-check-all-num-for-matching-do In Fortran 77, a numbered 'do' statement is ended by any statement with a matching line number. It is common (but not compulsory) to use a 'continue' statement for this purpose. If this variable has a non-nil value, indenting any numbered statement must check for a 'do' that ends there. If you always end 'do' statements with a 'continue' line (or if you use the more modern 'enddo'), then you can speed up indentation by setting this variable to nil (the default). fortran-blink-matching-if If this is t, indenting an 'endif' (or 'enddo' statement moves the cursor momentarily to the matching 'if' (or 'do') statement to show where it is. The default is nil. fortran-minimum-statement-indent-fixed Minimum indentation for Fortran statements when using fixed form continuation line style. Statement bodies are never indented by less than this. The default is 6. fortran-minimum-statement-indent-tab Minimum indentation for Fortran statements for tab format continuation line style. Statement bodies are never indented by less than this. The default is 8.

The following section describes the variables controlling the indentation of comments.

Several additional variables control how Fortran indentation works:

 fortran-do-indent Extra indentation within each level of 'do' statement (default 3). fortran-if-indent Extra indentation within each level of 'if', 'select case', or 'where' statements (default 3). fortran-structure-indent Extra indentation within each level of 'structure', 'union', 'map', or 'interface' statements (default 3). fortran-continuation-indent Extra indentation for bodies of continuation lines (default 5). fortran-check-all-num-for-matching-do In Fortran 77, a numbered 'do' statement is ended by any statement with a matching line number. It is common (but not compulsory) to use a 'continue' statement for this purpose. If this variable has a non-nil value, indenting any numbered statement must check for a 'do' that ends there. If you always end 'do' statements with a 'continue' line (or if you use the more modern 'enddo'), then you can speed up indentation by setting this variable to nil (the default). fortran-blink-matching-if If this is t, indenting an 'endif' (or 'enddo' statement moves the cursor momentarily to the matching 'if' (or 'do') statement to show where it is. The default is nil. fortran-minimum-statement-indent-fixed Minimum indentation for Fortran statements when using fixed form continuation line style. Statement bodies are never indented by less than this. The default is 6. fortran-minimum-statement-indent-tab Minimum indentation for Fortran statements for tab format continuation line style. Statement bodies are never indented by less than this. The default is 8.

The following section describes the variables controlling the indentation of comments.

## Auto Fill in Fortran Mode

Fortran mode has specialized support for Auto Fill mode, which is a minor mode that automatically splits statements as you insert them when they become too wide. Splitting a statement involves making continuation lines using fortran-continuation-string (see ForIndent Cont). This splitting happens when you type <SPC>, <RET>, or <TAB>, and also in the Fortran indentation commands. You activate Auto Fill in Fortran mode in the normal way. See Auto Fill.

Auto Fill breaks lines at spaces or delimiters when the lines get longer than the desired width (the value of fill-column). The delimiters (besides whitespace) that Auto Fill can break at are '+', '-', '/', '*', '=', '<', '>', and ','. The line break comes after the delimiter if the variable fortran-break-before-delimiters is nil. Otherwise, (and by default), the break comes before the delimiter.

To enable Auto Fill in all Fortran buffers, add auto-fill-mode to fortran-mode-hook. See Hooks.

## Checking Columns in Fortran

In standard Fortran 77, anything beyond column 72 is ignored. Most compilers provide an option to change this (for example, '-ffixed-line-length-N' in gfortran). Customize the variable fortran-line-length to change the line length in Fortran mode. Anything beyond this point is font-locked as a comment. (Unless it is inside a string: strings that extend beyond fortran-line-length will confuse font-lock.)

 C-c C-r Display a "column ruler" momentarily above the current line (fortran-column-ruler). C-c C-w Split the current window horizontally temporarily so that it is fortran-line-length columns wide (fortran-window-create-momentarily). This may help you avoid making lines longer than the limit imposed by your Fortran compiler. C-u C-c C-w Split the current window horizontally so that it is fortran-line-length columns wide (fortran-window-create). You can then continue editing. M-x fortran-strip-sequence-nos Delete all text in column fortran-line-length and beyond.

The command C-c C-r (fortran-column-ruler) shows a column ruler momentarily above the current line. The comment ruler is two lines of text that show you the locations of columns with special significance in Fortran programs. Square brackets show the limits of the columns for line numbers, and curly brackets show the limits of the columns for the statement body. Column numbers appear above them.

Note that the column numbers count from zero, as always in GNU Emacs. As a result, the numbers may be one less than those you are familiar with; but the positions they indicate in the line are standard for Fortran.

The text used to display the column ruler depends on the value of the variable indent-tabs-mode. If indent-tabs-mode is nil, then the value of the variable fortran-column-ruler-fixed is used as the column ruler. Otherwise, the value of the variable fortran-column-ruler-tab is displayed. By changing these variables, you can change the column ruler display.

C-c C-w (fortran-window-create-momentarily) temporarily splits the current window horizontally, making a window fortran-line-length columns wide, so you can see any lines that are too long. Type a space to restore the normal width.

You can also split the window horizontally and continue editing with the split in place. To do this, use C-u C-c C-w (M-x fortran-window-create). By editing in this window you can immediately see when you make a line too wide to be correct Fortran.

The command M-x fortran-strip-sequence-nos deletes all text in column fortran-line-length and beyond, on all lines in the current buffer. This is the easiest way to get rid of old sequence numbers.

## Fortran Keyword Abbrevs

Fortran mode provides many built-in abbrevs for common keywords and declarations. These are the same sort of abbrev that you can define yourself. To use them, you must turn on Abbrev mode. See Abbrevs.

The built-in abbrevs are unusual in one way: they all start with a semicolon. For example, one built-in Fortran abbrev is ';c' for 'continue'. If you insert ';c' and then insert a punctuation character such as a space or a newline, the ';c' expands automatically to 'continue', provided Abbrev mode is enabled.

Type ';?' or ';C-h' to display a list of all the built-in Fortran abbrevs and what they stand for.

## Compiling and Testing Programs

The previous chapter discusses the Emacs commands that are useful for making changes in programs. This chapter deals with commands that assist in the process of compiling and testing programs.

• Compilation: Compiling programs in languages other than Lisp (C, Pascal, etc.).
• Compilation Mode: The mode for visiting compiler errors.
• Compilation Shell: Customizing your shell properly for use in the compilation buffer.
• Grep Searching: Searching with grep.
• Flymake: Finding syntax errors on the fly.
• Debuggers: Running symbolic debuggers for non-Lisp programs.
• Executing Lisp: Various modes for editing Lisp programs, with different facilities for running the Lisp programs.
• Libraries: How Lisp programs are loaded into Emacs.
• Eval: Executing a single Lisp expression in Emacs.
• Interaction: Executing Lisp in an Emacs buffer.
• External Lisp: Communicating through Emacs with a separate Lisp.

## Running Compilations under Emacs

Emacs can run compilers for languages such as C and Fortran, feeding the compilation log into an Emacs buffer. It can also parse the error messages and show you where the errors occurred.

 M-x compile Run a compiler asynchronously under Emacs, with error messages going to the *compilation* buffer. M-x recompile Invoke a compiler with the same command as in the last invocation of M-x compile. M-x kill-compilation Kill the running compilation subprocess.

To run make or another compilation command, type M-x compile. This reads a shell command line using the minibuffer, and then executes the command by running a shell as a subprocess (or inferior process) of Emacs. The output is inserted in a buffer named *compilation*. The current buffer's default directory is used as the working directory for the execution of the command; normally, therefore, compilation takes place in this directory.

The default compilation command is 'make -k', which is usually correct for programs compiled using the make utility (the '-k' flag tells make to continue compiling as much as possible after an error). If you have done M-x compile before, the command that you specified is automatically stored in the variable compile-command; this is used as the default the next time you type M-x compile. A file can also specify a file-local value for compile-command (see File Variables).

Starting a compilation displays the *compilation* buffer in another window but does not select it. While the compilation is running, the word 'run' is shown in the major mode indicator for the *compilation* buffer, and the word 'Compiling' appears in all mode lines. You do not have to keep the *compilation* buffer visible while compilation is running; it continues in any case. When the compilation ends, for whatever reason, the mode line of the *compilation* buffer changes to say 'exit' (followed by the exit code: '[0]' for a normal exit), or 'signal' (if a signal terminated the process).

If you want to watch the compilation transcript as it appears, switch to the *compilation* buffer and move point to the end of the buffer. When point is at the end, new compilation output is inserted above point, which remains at the end. Otherwise, point remains fixed while compilation output is added at the end of the buffer.

If you change the variable compilation-scroll-output to a non-nil value, the *compilation* buffer scrolls automatically to follow the output. If the value is first-error, scrolling stops when the first error appears, leaving point at that error. For any other non-nil value, scrolling continues until there is no more output.

To rerun the last compilation with the same command, type M-x recompile. This reuses the compilation command from the last invocation of M-x compile. It also reuses the *compilation* buffer and starts the compilation in its default directory, which is the directory in which the previous compilation was started.

Starting a new compilation also kills any compilation already running in *compilation*, as the buffer can only handle one compilation at any time. However, M-x compile asks for confirmation before actually killing a compilation that is running; to always automatically kill the compilation without asking, change the variable compilation-always-kill to t. You can also kill a compilation process with the command M-x kill-compilation.

To run two compilations at once, start the first one, then rename the *compilation* buffer (perhaps using rename-uniquely; see Misc Buffer), then switch buffers and start the other compilation. This will create a new *compilation* buffer.

You can control the environment passed to the compilation command with the variable compilation-environment. Its value is a list of environment variable settings; each element should be a string of the form "envvarname=value". These environment variable settings override the usual ones.

## Compilation Mode

The *compilation* buffer uses a major mode called Compilation mode. Compilation mode turns each error message in the buffer into a hyperlink; you can move point to it and type <RET>, or click on it with the mouse (see Mouse References), to visit the locus of the error message in a separate window. The locus is the specific position in a file where that error occurred.

If you change the variable compilation-auto-jump-to-first-error to a non-nil value, Emacs automatically visits the locus of the first error message that appears in the *compilation* buffer.

Compilation mode provides the following additional commands. These commands can also be used in *grep* buffers, where the hyperlinks are search matches rather than error messages (see Grep Searching).

 M-g M-n, M-g n, C-x  Visit the locus of the next error message or match (next-error). M-g M-p, M-g p Visit the locus of the previous error message or match (previous-error). M-n Move point to the next error message or match, without visiting its locus (compilation-next-error). M-p Move point to the previous error message or match, without visiting its locus (compilation-previous-error). M-} Move point to the next error message or match occurring in a different file (compilation-next-file). M-{ Move point to the previous error message or match occurring in a different file (compilation-previous-file). C-c C-f Toggle Next Error Follow minor mode, which makes cursor motion in the compilation buffer produce automatic source display.

To visit errors sequentially, type C-x  (next-error), or equivalently M-g M-n or M-g n. This command can be invoked from any buffer, not just a Compilation mode buffer. The first time you invoke it after a compilation, it visits the locus of the first error message. Each subsequent C-x  visits the next error, in a similar fashion. If you visit a specific error with <RET> or a mouse click in the *compilation* buffer, subsequent C-x  commands advance from there. When C-x  finds no more error messages to visit, it signals an error. C-u C-x  starts again from the beginning of the compilation buffer, and visits the first locus.

M-g M-p or M-g p (previous-error) iterates through errors in the opposite direction.

The next-error and previous-error commands don't just act on the errors or matches listed in *compilation* and *grep* buffers; they also know how to iterate through error or match lists produced by other commands, such as M-x occur (see Other Repeating Search). If you are already in a buffer containing error messages or matches, those are the ones that are iterated through; otherwise, Emacs looks for a buffer containing error messages or matches amongst the windows of the selected frame, then for one that next-error or previous-error previously iterated through, and finally amongst all other buffers. If the buffer chosen for iterating through is not currently displayed in a window, it will be displayed.

By default, the next-error and previous-error commands skip less important messages. The variable compilation-skip-threshold controls this. The default value, 1, means to skip anything less important than a warning. A value of 2 means to skip anything less important than an error, while 0 means not to skip any messages.

When Emacs visits the locus of an error message, it momentarily highlights the relevant source line. The duration of this highlight is determined by the variable next-error-highlight.

If the *compilation* buffer is shown in a window with a left fringe (see Fringes), the locus-visiting commands put an arrow in the fringe, pointing to the current error message. If the window has no left fringe, such as on a text terminal, these commands scroll the window so that the current message is at the top of the window. If you change the variable compilation-context-lines to an integer value n, these commands scroll the window so that the current error message is n lines from the top, whether or not there is a fringe; the default value, nil, gives the behavior described above.

To parse messages from the compiler, Compilation mode uses the variable compilation-error-regexp-alist which lists various error message formats and tells Emacs how to extract the locus from each. A similar variable, grep-regexp-alist, tells Emacs how to parse output from a grep command (see Grep Searching).

Compilation mode also defines the keys <SPC> and <DEL> to scroll by screenfuls; M-n (compilation-next-error) and M-p (compilation-previous-error) to move to the next or previous error message; and M-{ (compilation-next-file) and M-} (compilation-previous-file) to move to the next or previous error message for a different source file.

You can type C-c C-f to toggle Next Error Follow mode. In this minor mode, ordinary cursor motion in the compilation buffer automatically updates the source buffer, i.e., moving the cursor over an error message causes the locus of that error to be displayed.

The features of Compilation mode are also available in a minor mode called Compilation Minor mode. This lets you parse error messages in any buffer, not just a normal compilation output buffer. Type M-x compilation-minor-mode to enable the minor mode. For instance, in an Rlogin buffer (see Remote Host), Compilation minor mode automatically accesses remote source files by FTP (see File Names).

## Subshells For Compilation

The M-x compile command uses a shell to run the compilation command, but specifies the option for a noninteractive shell. This means, in particular, that the shell should start with no prompt. If you find your usual shell prompt making an unsightly appearance in the *compilation* buffer, it means you have made a mistake in your shell's init file by setting the prompt unconditionally. (This init file may be named .bashrc, .profile, .cshrc, .shrc, etc., depending on what shell you use.) The shell init file should set the prompt only if there already is a prompt. Here's how to do it in bash:

if [ "${PS1+set}" = set ] then PS1=... fi  And here's how to do it in csh: if ($?prompt) set prompt = ...

Emacs does not expect a compiler process to launch asynchronous subprocesses; if it does, and they keep running after the main compiler process has terminated, Emacs may kill them or their output may not arrive in Emacs. To avoid this problem, make the main compilation process wait for its subprocesses to finish. In a shell script, you can do this using '$!' and 'wait', like this: (sleep 10; echo 2nd)& pid=$!  # Record pid of subprocess
echo first message
wait $pid # Wait for subprocess  If the background process does not output to the compilation buffer, so you only need to prevent it from being killed when the main compilation process terminates, this is sufficient: nohup command; sleep 1  On MS-DOS, asynchronous subprocesses are not supported, so M-x compile runs the compilation command synchronously (i.e., you must wait until the command finishes before you can do anything else in Emacs). ## Searching With Grep Under Emacs Just as you can run a compiler from Emacs and then visit the lines with compilation errors, you can also run grep and then visit the lines on which matches were found. This works by treating the matches reported by grep as if they were "errors". The output buffer uses Grep mode, which is a variant of Compilation mode (see Compilation Mode).  M-x grep, M-x lgrep Run grep asynchronously under Emacs, listing matching lines in the buffer named *grep*. M-x grep-find, M-x find-grep, M-x rgrep Run grep via find, and collect output in the *grep* buffer. M-x zrgrep Run zgrep and collect output in the *grep* buffer. M-x kill-grep Kill the running grep subprocess. To run grep, type M-x grep, then enter a command line that specifies how to run grep. Use the same arguments you would give grep when running it normally: a grep-style regexp (usually in single-quotes to quote the shell's special characters) followed by file names, which may use wildcards. If you specify a prefix argument for M-x grep, it finds the tag (see Tags) in the buffer around point, and puts that into the default grep command. Your command need not run grep; you can use any shell command that produces output in the same format. For instance, you can chain grep commands, like this: grep -nH -e foo *.el | grep bar | grep toto  The output from grep goes in the *grep* buffer. You can find the corresponding lines in the original files using C-x , <RET>, and so forth, just like compilation errors. Some grep programs accept a '--color' option to output special markers around matches for the purpose of highlighting. You can make use of this feature by setting grep-highlight-matches to t. When displaying a match in the source buffer, the exact match will be highlighted, instead of the entire source line. The command M-x grep-find (also available as M-x find-grep) is similar to M-x grep, but it supplies a different initial default for the command—one that runs both find and grep, so as to search every file in a directory tree. See also the find-grep-dired command, in Dired and Find. The commands M-x lgrep (local grep) and M-x rgrep (recursive grep) are more user-friendly versions of grep and grep-find, which prompt separately for the regular expression to match, the files to search, and the base directory for the search. Case sensitivity of the search is controlled by the current value of case-fold-search. The command M-x zrgrep is similar to M-x rgrep, but it calls zgrep instead of grep to search the contents of gzipped files. These commands build the shell commands based on the variables grep-template (for lgrep) and grep-find-template (for rgrep). The files to search can use aliases defined in the variable grep-files-aliases. Directories listed in the variable grep-find-ignored-directories are automatically skipped by M-x rgrep. The default value includes the data directories used by various version control systems. ## Finding Syntax Errors on the Fly Flymake mode is a minor mode that performs on-the-fly syntax checking for many programming and markup languages, including C, C++, Perl, HTML, and TeX/LaTeX. It is somewhat analogous to Flyspell mode, which performs spell checking for ordinary human languages in a similar fashion (see Spelling). As you edit a file, Flymake mode runs an appropriate syntax checking tool in the background, using a temporary copy of the buffer. It then parses the error and warning messages, and highlights the erroneous lines in the buffer. The syntax checking tool used depends on the language; for example, for C/C++ files this is usually the C compiler. Flymake can also use build tools such as make for checking complicated projects. To enable Flymake mode, type M-x flymake-mode. You can jump to the errors that it finds by using M-x flymake-goto-next-error and M-x flymake-goto-prev-error. To display any error messages associated with the current line, type M-x flymake-display-err-menu-for-current-line. ## Running Debuggers under Emacs The GUD (Grand Unified Debugger) library provides an Emacs interface to a wide variety of symbolic debuggers. It can run the GNU Debugger (GDB), as well as DBX, SDB, XDB, Perl's debugging mode, the Python debugger PDB, and the Java Debugger JDB. Emacs provides a special interface to GDB, which uses extra Emacs windows to display the state of the debugged program. See GDB Graphical Interface. Emacs also has a built-in debugger for Emacs Lisp programs. ## Starting GUD There are several commands for starting a debugger subprocess, each corresponding to a particular debugger program.  M-x gdb Run GDB as a subprocess, and interact with it via an IDE-like Emacs interface. See GDB Graphical Interface, for more information about this command. M-x gud-gdb Run GDB, using a GUD interaction buffer for input and output to the GDB subprocess (see Debugger Operation). If such a buffer already exists, switch to it; otherwise, create the buffer and switch to it. The other commands in this list do the same, for other debugger programs. M-x perldb Run the Perl interpreter in debug mode. M-x jdb Run the Java debugger. M-x pdb Run the Python debugger. M-x dbx Run the DBX debugger. M-x xdb Run the XDB debugger. M-x sdb Run the SDB debugger. Each of these commands reads a command line to invoke the debugger, using the minibuffer. The minibuffer's initial contents contain the standard executable name and options for the debugger, and sometimes also a guess for the name of the executable file you want to debug. Shell wildcards and variables are not allowed in this command line. Emacs assumes that the first command argument which does not start with a '-' is the executable file name. Tramp provides a facility for remote debugging, whereby both the debugger and the program being debugged are on the same remote host. This is separate from GDB's remote debugging feature, where the program and the debugger run on different machines. ## Debugger Operation The GUD interaction buffer is an Emacs buffer that is used to send text commands to a debugger subprocess, and record its output. This is the basic interface for interacting with a debugger, used by M-x gud-gdb and other commands listed in Starting GUD. The M-x gdb command extends this interface with additional specialized buffers for controlling breakpoints, stack frames, and other aspects of the debugger state (see GDB Graphical Interface). The GUD interaction buffer uses a variant of Shell mode, so the Emacs commands defined by Shell mode are available (see Shell Mode). Completion is available for most debugger commands (see Completion), and you can use the usual Shell mode history commands to repeat them. See Commands of GUD, for special commands that can be used in the GUD interaction buffer. As you debug a program, Emacs displays the relevant source files by visiting them in Emacs buffers, with an arrow in the left fringe indicating the current execution line. (On a text terminal, the arrow appears as '=>', overlaid on the first two text columns.) Moving point in such a buffer does not move the arrow. You are free to edit these source files, but note that inserting or deleting lines will throw off the arrow's positioning, as Emacs has no way to figure out which edited source line corresponds to the line reported by the debugger subprocess. To update this information, you typically have to recompile and restart the program. GUD Tooltip mode is a global minor mode that adds tooltip support to GUD. To toggle this mode, type M-x gud-tooltip-mode. It is disabled by default. If enabled, you can move the mouse cursor over a variable, a function, or a macro (collectively called identifiers) to show their values in tooltips (see Tooltips). Alternatively, mark an identifier or an expression by dragging the mouse over it, then leave the mouse in the marked area to have the value of the expression displayed in a tooltip. The GUD Tooltip mode takes effect in the GUD interaction buffer, and in all source buffers with major modes listed in the variable gud-tooltip-modes. If the variable gud-tooltip-echo-area is non-nil, or if you turned off the tooltip mode, values are shown in the echo area instead of a tooltip. When using GUD Tooltip mode with M-x gud-gdb, displaying an expression's value in GDB can sometimes expand a macro, potentially causing side effects in the debugged program. For that reason, using tooltips in gud-gdb is disabled. If you use the M-x gdb interface, this problem does not occur, as there is special code to avoid side-effects; furthermore, you can display macro definitions associated with an identifier when the program is not executing. ## Commands of GUD GUD provides commands for setting and clearing breakpoints, selecting stack frames, and stepping through the program.  C-x Set a breakpoint on the source line that point is on. C-x <SPC> (gud-break), when called in a source buffer, sets a debugger breakpoint on the current source line. This command is available only after starting GUD. If you call it in a buffer that is not associated with any debugger subprocess, it signals a error. The following commands are available both in the GUD interaction buffer and globally, but with different key bindings. The keys starting with C-c are available only in the GUD interaction buffer, while those starting with C-x C-a are available globally. Some of these commands are also available via the tool bar; some are not supported by certain debuggers.  C-c C-l, C-x C-a C-l Display, in another window, the last source line referred to in the GUD interaction buffer (gud-refresh). C-c C-s, C-x C-a C-s Execute the next single line of code (gud-step). If the line contains a function call, execution stops after entering the called function. C-c C-n, C-x C-a C-n Execute the next single line of code, stepping across function calls without stopping inside the functions (gud-next). C-c C-i, C-x C-a C-i Execute a single machine instruction (gud-stepi). C-c C-p, C-x C-a C-p Evaluate the expression at point (gud-print). If Emacs does not print the exact expression that you want, mark it as a region first. C-c C-r, C-x C-a C-r Continue execution without specifying any stopping point. The program will run until it hits a breakpoint, terminates, or gets a signal that the debugger is checking for (gud-cont). C-c C-d, C-x C-a C-d Delete the breakpoint(s) on the current source line, if any (gud-remove). If you use this command in the GUD interaction buffer, it applies to the line where the program last stopped. C-c C-t, C-x C-a C-t Set a temporary breakpoint on the current source line, if any (gud-tbreak). If you use this command in the GUD interaction buffer, it applies to the line where the program last stopped. C-c <, C-x C-a < Select the next enclosing stack frame (gud-up). This is equivalent to the GDB command 'up'. C-c >, C-x C-a > Select the next inner stack frame (gud-down). This is equivalent to the GDB command 'down'. C-c C-u, C-x C-a C-u Continue execution to the current line (gud-until). The program will run until it hits a breakpoint, terminates, gets a signal that the debugger is checking for, or reaches the line on which the cursor currently sits. C-c C-f, C-x C-a C-f Run the program until the selected stack frame returns or stops for some other reason (gud-finish). If you are using GDB, these additional key bindings are available:  C-x C-a C-j Only useful in a source buffer, gud-jump transfers the program's execution point to the current line. In other words, the next line that the program executes will be the one where you gave the command. If the new execution line is in a different function from the previously one, GDB prompts for confirmation since the results may be bizarre. See the GDB manual entry regarding jump for details. With GDB, complete a symbol name (gud-gdb-complete-command). This key is available only in the GUD interaction buffer. These commands interpret a numeric argument as a repeat count, when that makes sense. Because <TAB> serves as a completion command, you can't use it to enter a tab as input to the program you are debugging with GDB. Instead, type C-q <TAB> to enter a tab. ## GUD Customization On startup, GUD runs one of the following hooks: gdb-mode-hook, if you are using GDB; dbx-mode-hook, if you are using DBX; sdb-mode-hook, if you are using SDB; xdb-mode-hook, if you are using XDB; perldb-mode-hook, for Perl debugging mode; pdb-mode-hook, for PDB; jdb-mode-hook, for JDB. See Hooks. The gud-def Lisp macro provides a convenient way to define an Emacs command that sends a particular command string to the debugger, and set up a key binding for in the GUD interaction buffer: (gud-def function cmdstring binding docstring)  This defines a command named function which sends cmdstring to the debugger process, and gives it the documentation string docstring. You can then use the command function in any buffer. If binding is non-nil, gud-def also binds the command to C-c binding in the GUD buffer's mode and to C-x C-a binding generally. The command string cmdstring may contain certain '%'-sequences that stand for data to be filled in at the time function is called:  '%f' The name of the current source file. If the current buffer is the GUD buffer, then the "current source file" is the file that the program stopped in. '%l' The number of the current source line. If the current buffer is the GUD buffer, then the "current source line" is the line that the program stopped in. '%e' In transient-mark-mode the text in the region, if it is active. Otherwise, the text of the C lvalue or function-call expression at or adjacent to point. '%a' The text of the hexadecimal address at or adjacent to point. '%p' The numeric argument of the called function, as a decimal number. If the command is used without a numeric argument, '%p' stands for the empty string. If you don't use '%p' in the command string, the command you define ignores any numeric argument. '%d' The name of the directory of the current source file. '%c' Fully qualified class name derived from the expression surrounding point (jdb only). ## GDB Graphical Interface The command M-x gdb starts GDB in an IDE-like interface, with specialized buffers for controlling breakpoints, stack frames, and other aspects of the debugger state. It also provides additional ways to control the debugging session with the mouse, such as clicking in the fringe of a source buffer to set a breakpoint there. To run GDB using just the GUD interaction buffer interface, without these additional features, use M-x gud-gdb (see Starting GUD). You must use this if you want to debug multiple programs within one Emacs session, as that is currently unsupported by M-x gdb. Internally, M-x gdb informs GDB that its "screen size" is unlimited; for correct operation, you must not change GDB's screen height and width values during the debugging session. ## GDB User Interface Layout If the variable gdb-many-windows is nil (the default), M-x gdb normally displays only the GUD interaction buffer. However, if the variable gdb-show-main is also non-nil, it starts with two windows: one displaying the GUD interaction buffer, and the other showing the source for the main function of the program you are debugging. If gdb-many-windows is non-nil, then M-x gdb displays the following frame layout:  +--------------------------------+--------------------------------+ | GUD interaction buffer | Locals/Registers buffer | |--------------------------------+--------------------------------+ | Primary Source buffer | I/O buffer for debugged pgm | |--------------------------------+--------------------------------+ | Stack buffer | Breakpoints/Threads buffer | +--------------------------------+--------------------------------+  If you ever change the window layout, you can restore the "many windows" layout by typing M-x gdb-restore-windows. To toggle between the many windows layout and a simple layout with just the GUD interaction buffer and a source file, type M-x gdb-many-windows. You may also specify additional GDB-related buffers to display, either in the same frame or a different one. Select the buffers you want by typing M-x gdb-display-buffertype-buffer or M-x gdb-frame-buffertype-buffer, where buffertype is the relevant buffer type, such as 'breakpoints'. You can do the same with the menu bar, with the 'GDB-Windows' and 'GDB-Frames' sub-menus of the 'GUD' menu. When you finish debugging, kill the GUD interaction buffer with C-x k, which will also kill all the buffers associated with the session. However, you need not do this if, after editing and re-compiling your source code within Emacs, you wish to continue debugging. When you restart execution, GDB automatically finds the new executable. Keeping the GUD interaction buffer has the advantage of keeping the shell history as well as GDB's breakpoints. You do need to check that the breakpoints in recently edited source files are still in the right places. ## Source Buffers  Mouse-1 (in fringe) Set or clear a breakpoint on that line. C-Mouse-1 (in fringe) Enable or disable a breakpoint on that line. Mouse-3 (in fringe) Continue execution to that line. C-Mouse-3 (in fringe) Jump to that line. On a graphical display, you can click Mouse-1 in the fringe of a source buffer, to set a breakpoint on that line (see Fringes). A red dot appears in the fringe, where you clicked. If a breakpoint already exists there, the click removes it. A C-Mouse-1 click enables or disables an existing breakpoint; a breakpoint that is disabled, but not unset, is indicated by a gray dot. On a text terminal, or when fringes are disabled, enabled breakpoints are indicated with a 'B' character in the left margin of the window. Disabled breakpoints are indicated with 'b'. (The margin is only displayed if a breakpoint is present.) A solid arrow in the left fringe of a source buffer indicates the line of the innermost frame where the debugged program has stopped. A hollow arrow indicates the current execution line of a higher-level frame. If you drag the arrow in the fringe with Mouse-1, that causes execution to advance to the line where you release the button. Alternatively, you can click Mouse-3 in the fringe to advance to that line. You can click C-Mouse-3 in the fringe to jump to that line without executing the intermediate lines. This command allows you to go backwards, which can be useful for running through code that has already executed, to examine its execution in more detail. ## Breakpoints Buffer The GDB Breakpoints buffer shows the breakpoints, watchpoints and catchpoints in the debugger session. It provides the following commands, which mostly apply to the current breakpoint (the breakpoint which point is on):  Enable/disable current breakpoint (gdb-toggle-breakpoint). On a graphical display, this changes the color of the dot in the fringe of the source buffer at that line. The dot is red when the breakpoint is enabled, and gray when it is disabled. D Delete the current breakpoint (gdb-delete-breakpoint). Visit the source line for the current breakpoint (gdb-goto-breakpoint). Mouse-2 Visit the source line for the breakpoint you click on. When gdb-many-windows is non-nil, the GDB Breakpoints buffer shares its window with the GDB Threads buffer. To switch from one to the other click with Mouse-1 on the relevant button in the header line. If gdb-show-threads-by-default is non-nil, the GDB Threads buffer is the one shown by default. ## Threads Buffer The GDB Threads buffer displays a summary of the threads in the debugged program. To select a thread, move point there and type <RET> (gdb-select-thread), or click on it with Mouse-2. This also displays the associated source buffer, and updates the contents of the other GDB buffers. You can customize variables under gdb-buffers group to select fields included in GDB Threads buffer.  gdb-thread-buffer-verbose-names Show long thread names like 'Thread 0x4e2ab70 (LWP 1983)'. gdb-thread-buffer-arguments Show arguments of thread top frames. gdb-thread-buffer-locations Show file information or library names. gdb-thread-buffer-addresses Show addresses for thread frames in threads buffer. To view information for several threads simultaneously, use the following commands from the GDB Threads buffer.  d Display disassembly buffer for the thread at current line (gdb-display-disassembly-for-thread). f Display the GDB Stack buffer for the thread at current line (gdb-display-stack-for-thread). l Display the GDB Locals buffer for the thread at current line (gdb-display-locals-for-thread). r Display the GDB Registers buffer for the thread at current line (gdb-display-registers-for-thread). Their upper-case counterparts, D, F,L and R, display the corresponding buffer in a new frame. When you create a buffer showing information about some specific thread, it becomes bound to that thread and keeps showing actual information while you debug your program. The mode indicator for each GDB buffer shows the number of thread it is showing information about. The thread number is also included in the buffer name of bound buffers. Further commands are available in the GDB Threads buffer which depend on the mode of GDB that is used for controlling execution of your program. See Multithreaded Debugging. ## Stack Buffer The GDB Stack buffer displays a call stack, with one line for each of the nested subroutine calls (stack frames) in the debugger session. On graphical displays, the selected stack frame is indicated by an arrow in the fringe. On text terminals, or when fringes are disabled, the selected stack frame is displayed in reverse contrast. To select a stack frame, move point in its line and type <RET> (gdb-frames-select), or click Mouse-2 on it. Doing so also updates the Locals buffer (see Other GDB Buffers). ## Other GDB Buffers • Locals Buffer: This buffer displays the values of local variables of the current frame for simple data types. Press <RET> or click Mouse-2 on the value if you want to edit it. Arrays and structures display their type only. With GDB 6.4 or later, you can examine the value of the local variable at point by typing <RET>, or with a Mouse-2 click. With earlier versions of GDB, use <RET> or Mouse-2 on the type description ('[struct/union]' or '[array]'). See Watch Expressions. • Registers Buffer: This buffer displays the values held by the registers (see Registers). Press <RET> or click Mouse-2 on a register if you want to edit its value. With GDB 6.4 or later, recently changed register values display with font-lock-warning-face. • Assembler Buffer:The assembler buffer displays the current frame as machine code. An arrow points to the current instruction, and you can set and remove breakpoints as in a source buffer. Breakpoint icons also appear in the fringe or margin. • Memory Buffer: The memory buffer lets you examine sections of program memory. Click Mouse-1 on the appropriate part of the header line to change the starting address or number of data items that the buffer displays. Alternatively, use S or N respectively. Click Mouse-3 on the header line to select the display format or unit size for these data items. When gdb-many-windows is non-nil, the locals buffer shares its window with the registers buffer, just like breakpoints and threads buffers. To switch from one to the other, click with Mouse-1 on the relevant button in the header line. ## Watch Expressions If you want to see how a variable changes each time your program stops, move point into the variable name and click on the watch icon in the tool bar (gud-watch) or type C-x C-a C-w. If you specify a prefix argument, you can enter the variable name in the minibuffer. Each watch expression is displayed in the speedbar (see Speedbar). Complex data types, such as arrays, structures and unions are represented in a tree format. Leaves and simple data types show the name of the expression and its value and, when the speedbar frame is selected, display the type as a tooltip. Higher levels show the name, type and address value for pointers and just the name and type otherwise. Root expressions also display the frame address as a tooltip to help identify the frame in which they were defined. To expand or contract a complex data type, click Mouse-2 or press <SPC> on the tag to the left of the expression. Emacs asks for confirmation before expanding the expression if its number of immediate children exceeds the value of the variable gdb-max-children. To delete a complex watch expression, move point to the root expression in the speedbar and type D (gdb-var-delete). To edit a variable with a simple data type, or a simple element of a complex data type, move point there in the speedbar and type <RET> (gdb-edit-value). Or you can click Mouse-2 on a value to edit it. Either way, this reads the new value using the minibuffer. If you set the variable gdb-show-changed-values to non-nil (the default value), Emacs uses font-lock-warning-face to highlight values that have recently changed and shadow face to make variables which have gone out of scope less noticeable. When a variable goes out of scope you can't edit its value. If the variable gdb-delete-out-of-scope is non-nil (the default value), Emacs automatically deletes watch expressions which go out of scope. Sometimes, when re-entering the same function, it may be useful to set this value to nil so that you don't need to recreate the watch expression. If the variable gdb-use-colon-colon-notation is non-nil, Emacs uses the 'function::variable' format. This allows the user to display watch expressions which share the same variable name. The default value is nil. To automatically raise the speedbar every time the display of watch expressions updates, set gdb-speedbar-auto-raise to non-nil. This can be useful if you are debugging with a full screen Emacs frame. ## Multithreaded Debugging In GDB's all-stop mode, whenever your program stops, all execution threads stop. Likewise, whenever you restart the program, all threads start executing. For some multi-threaded targets, GDB supports a further mode of operation, called non-stop mode, in which you can examine stopped program threads in the debugger while other threads continue to execute freely. Versions of GDB prior to 7.0 do not support non-stop mode, and it does not work on all targets. The variable gdb-non-stop-setting determines whether Emacs runs GDB in all-stop mode or non-stop mode. The default is t, which means it tries to use non-stop mode if that is available. If you change the value to nil, or if non-stop mode is unavailable, Emacs runs GDB in all-stop mode. The variable takes effect when Emacs begins a debugging session; if you change its value, you should restart any active debugging session. When a thread stops in non-stop mode, Emacs usually switches to that thread. If you don't want Emacs to do this switch if another stopped thread is already selected, change the variable gdb-switch-when-another-stopped to nil. Emacs can decide whether or not to switch to the stopped thread depending on the reason which caused the stop. Customize the variable gdb-switch-reasons to select the stop reasons which will cause a thread switch. The variable gdb-stopped-functions allows you to execute your functions whenever some thread stops. In non-stop mode, you can switch between different modes for GUD execution control commands.  Non-stop/A When gdb-gud-control-all-threads is t (the default value), interruption and continuation commands apply to all threads, so you can halt or continue all your threads with one command using gud-stop-subjob and gud-cont, respectively. The 'Go' button is shown on the toolbar when at least one thread is stopped, whereas 'Stop' button is shown when at least one thread is running. Non-stop/T When gdb-gud-control-all-threads is nil, only the current thread is stopped/continued. 'Go' and 'Stop' buttons on the GUD toolbar are shown depending on the state of current thread. You can change the current value of gdb-gud-control-all-threads from the tool bar or from 'GUD-GDB-MI' menu. Stepping commands always apply to the current thread. In non-stop mode, you can interrupt/continue your threads without selecting them. Hitting i in threads buffer interrupts thread under point, c continues it, s steps through. More such commands may be added in the future. Note that when you interrupt a thread, it stops with the 'signal received' reason. If that reason is included in your gdb-switch-reasons (it is by default), Emacs will switch to that thread. ## Executing Lisp Expressions Emacs has major modes for several variants of Lisp. They use the same editing commands as other programming language modes (see Programs). Also, they provide special commands for executing Lisp expressions.  Emacs Lisp mode The mode for editing Emacs Lisp source files. It defines C-M-x to evaluate the current top-level Lisp expression. See Lisp Eval. Lisp Interaction mode The mode for an interactive Emacs Lisp session. It defines C-j to evaluate the expression before point and insert its value in the buffer. See Lisp Interaction. Lisp mode The mode for editing source files of programs that run in Lisps other than Emacs Lisp. It defines C-M-x to evaluate the current top-level expression in an external Lisp. See External Lisp. Inferior Lisp mode The mode for an interactive session with an external Lisp that is being run as a subprocess (or inferior process) of Emacs. See External Lisp. Scheme mode Like Lisp mode, but for Scheme programs. Inferior Scheme mode Like Inferior Lisp mode, but for Scheme. ## Libraries of Lisp Code for Emacs Emacs Lisp code is stored in files whose names conventionally end in .el. Such files are automatically visited in Emacs Lisp mode. Emacs Lisp code can be compiled into byte-code, which loads faster, takes up less space, and executes faster. By convention, compiled Emacs Lisp code goes in a separate file whose name ends in '.elc'. For example, the compiled code for foo.el goes in foo.elc. To load an Emacs Lisp file, type M-x load-file. This command reads a file name using the minibuffer, and executes the contents of that file as Emacs Lisp code. It is not necessary to visit the file first; this command reads the file directly from disk, not from an existing Emacs buffer. If an Emacs Lisp file is installed in the Emacs Lisp load path (defined below), you can load it by typing M-x load-library, instead of using M-x load-file. The M-x load-library command prompts for a library name rather than a file name; it searches through each directory in the Emacs Lisp load path, trying to find a file matching that library name. If the library name is 'foo', it tries looking for files named foo.elc, foo.el, and lastly just foo; the first one found is loaded. This command prefers .elc files over .el files because compiled files load and run faster. If it finds that lib.el is newer than lib.elc, it issues a warning, in case someone made changes to the .el file and forgot to recompile it, but loads the .elc file anyway. (Due to this behavior, you can save unfinished edits to Emacs Lisp source files, and not recompile until your changes are ready for use.) Emacs Lisp programs usually load Emacs Lisp files using the load function. This is similar to load-library, but is lower-level and accepts additional arguments. The Emacs Lisp load path is specified by the variable load-path. Its value should be a list of directory names (strings). These directories are searched, in the specified order, by the M-x load-library command, the lower-level load function, and other Emacs functions that find Emacs Lisp libraries. A list entry in load-path can also have the special value nil, which stands for the current default directory, but it is almost always a bad idea to use this. (If you find yourself wishing that nil were in the list, most likely what you really want is to use M-x load-file.) The default value of load-path is a list of directories where the Lisp code for Emacs itself is stored. If you have libraries in another directory, you can add that directory to the load path. Unlike most other variables described in this manual, load-path cannot be changed via the Customize interface (see Easy Customization), but you can add a directory to it by putting a line like this in your init file (see Init File): (add-to-list 'load-path "/path/to/my/lisp/library")  Some commands are autoloaded; when you run them, Emacs automatically loads the associated library first. For instance, the M-x compile command (see Compilation) is autoloaded; if you call it, Emacs automatically loads the compile library first. In contrast, the command M-x recompile is not autoloaded, so it is unavailable until you load the compile library. Automatic loading can also occur when you look up the documentation of an autoloaded command (see Name Help), if the documentation refers to other functions and variables in its library (loading the library lets Emacs properly set up the hyperlinks in the *Help* buffer). To disable this feature, change the variable help-enable-auto-load to nil. By default, Emacs refuses to load compiled Lisp files which were compiled with XEmacs, a modified versions of Emacs—they can cause Emacs to crash. Set the variable load-dangerous-libraries to t if you want to try loading them. ## Evaluating Emacs Lisp Expressions Emacs Lisp mode is the major mode for editing Emacs Lisp. Its mode command is M-x emacs-lisp-mode. Emacs provides several commands for evaluating Emacs Lisp expressions. You can use these commands in Emacs Lisp mode, to test your Emacs Lisp code as it is being written. For example, after re-writing a function, you can evaluate the function definition to make it take effect for subsequent function calls. These commands are also available globally, and can be used outside Emacs Lisp mode.  M-: Read a single Emacs Lisp expression in the minibuffer, evaluate it, and print the value in the echo area (eval-expression). C-x C-e Evaluate the Emacs Lisp expression before point, and print the value in the echo area (eval-last-sexp). C-M-x (in Emacs Lisp mode), M-x eval-defun Evaluate the defun containing or after point, and print the value in the echo area (eval-defun). M-x eval-region Evaluate all the Emacs Lisp expressions in the region. M-x eval-buffer Evaluate all the Emacs Lisp expressions in the buffer. M-: (eval-expression) reads an expression using the minibuffer, and evaluates it. (Before evaluating the expression, the current buffer switches back to the buffer that was current when you typed M-:, not the minibuffer into which you typed the expression.) The command C-x C-e (eval-last-sexp) evaluates the Emacs Lisp expression preceding point in the buffer, and displays the value in the echo area. When the result of an evaluation is an integer, you can type C-x C-e a second time to display the value of the integer result in additional formats (octal, hexadecimal, and character). If M-: or C-x C-e is given a prefix argument, it inserts the value into the current buffer at point, rather than displaying it in the echo area. The argument's value does not matter. The eval-defun command is bound to C-M-x in Emacs Lisp mode. It evaluates the top-level Lisp expression containing or following point, and prints the value in the echo area. In this context, a top-level expression is referred to as a "defun", but it need not be an actual defun (function definition). In particular, this command treats defvar expressions specially. Normally, evaluating a defvar expression does nothing if the variable it defines already has a value. But this command unconditionally resets the variable to the initial value specified by the defvar; this is convenient for debugging Emacs Lisp programs. defcustom and defface expressions are treated similarly. Note that the other commands documented in this section do not have this special feature. With a prefix argument, C-M-x instruments the function definition for Edebug, the Emacs Lisp Debugger. The command M-x eval-region parses the text of the region as one or more Lisp expressions, evaluating them one by one. M-x eval-buffer is similar but evaluates the entire buffer. The options eval-expression-print-level and eval-expression-print-length control the maximum depth and length of lists to print in the result of the evaluation commands before abbreviating them. eval-expression-debug-on-error controls whether evaluation errors invoke the debugger when these commands are used; its default is t. ## Lisp Interaction Buffers When Emacs starts up, it contains a buffer named *scratch*, which is provided for evaluating Emacs Lisp expressions interactively. Its major mode is Lisp Interaction mode. You can also enable Lisp Interaction mode by typing M-x lisp-interaction-mode. In the *scratch* buffer, and other Lisp Interaction mode buffers, C-j (eval-print-last-sexp) evaluates the Lisp expression before point, and inserts the value at point. Thus, as you type expressions into the buffer followed by C-j after each expression, the buffer records a transcript of the evaluated expressions and their values. All other commands in Lisp Interaction mode are the same as in Emacs Lisp mode. At startup, the *scratch* buffer contains a short message, in the form of a Lisp comment, that explains what it is for. This message is controlled by the variable initial-scratch-message, which should be either a string, or nil (which means to suppress the message). An alternative way of evaluating Emacs Lisp expressions interactively is to use Inferior Emacs Lisp mode, which provides an interface rather like Shell mode (see Shell Mode) for evaluating Emacs Lisp expressions. Type M-x ielm to create an *ielm* buffer which uses this mode. ## Running an External Lisp Lisp mode is the major mode for editing programs written in general-purpose Lisp dialects, such as Common Lisp. Its mode command is M-x lisp-mode. Emacs uses Lisp mode automatically for files whose names end in .l, .lsp, or .lisp. You can run an external Lisp session as a subprocess or inferior process of Emacs, and pass expressions to it to be evaluated. To begin an external Lisp session, type M-x run-lisp. This runs the program named lisp, and sets it up so that both input and output go through an Emacs buffer named *inferior-lisp*. To change the name of the Lisp program run by M-x run-lisp, change the variable inferior-lisp-program. The major mode for the *lisp* buffer is Inferior Lisp mode, which combines the characteristics of Lisp mode and Shell mode (see Shell Mode). To send input to the Lisp session, go to the end of the *lisp* buffer and type the input, followed by <RET>. Terminal output from the Lisp session is automatically inserted in the buffer. When you edit a Lisp program in Lisp mode, you can type C-M-x (lisp-eval-defun) to send an expression from the Lisp mode buffer to a Lisp session that you had started with M-x run-lisp. The expression sent is the top-level Lisp expression at or following point. The resulting value goes as usual into the *inferior-lisp* buffer. Note that the effect of C-M-x in Lisp mode is thus very similar to its effect in Emacs Lisp mode (see Lisp Eval), except that the expression is sent to a different Lisp environment instead of being evaluated in Emacs. The facilities for editing Scheme code, and for sending expressions to a Scheme subprocess, are very similar. Scheme source files are edited in Scheme mode, which can be explicitly enabled with M-x scheme-mode. You can initiate a Scheme session by typing M-x run-scheme (the buffer for interacting with Scheme is named *scheme*), and send expressions to it by typing C-M-x. ## Maintaining Large Programs This chapter describes Emacs features for maintaining large programs. If you are maintaining a large Lisp program, then in addition to the features described here, you may find the ERT ("Emacs Lisp Regression Testing") library useful. • Version Control: Using version control systems. • Change Log: Maintaining a change history for your program. • Tags: Go directly to any function in your program in one command. Tags remembers which file it is in. • EDE: An integrated development environment for Emacs. • Emerge: A convenient way of merging two versions of a program. ## Version Control A version control system is a program that can record multiple versions of a source file, storing information such as the creation time of each version, who made it, and a description of what was changed. The Emacs version control interface is called VC. VC commands work with different version control systems; currently, it supports GNU Arch, Bazaar, CVS, Git, Mercurial, Monotone, RCS, SCCS/CSSC, and Subversion. Of these, the GNU project distributes CVS, Arch, RCS, and Bazaar. VC is enabled automatically whenever you visit a file governed by a version control system. To disable VC entirely, set the customizable variable vc-handled-backends to nil (see Customizing VC). ## Introduction to Version Control VC allows you to use a version control system from within Emacs, integrating the version control operations smoothly with editing. It provides a uniform interface for common operations in many version control operations. Some uncommon or intricate version control operations, such as altering repository settings, are not supported in VC. You should perform such tasks outside Emacs, e.g., via the command line. This section provides a general overview of version control, and describes the version control systems that VC supports. You can skip this section if you are already familiar with the version control system you want to use. ## Understanding Why To Use Version Control Version control systems provide you with three important capabilities: • Reversibility: the ability to back up to a previous state if you discover that some modification you did was a mistake or a bad idea. • Concurrency: the ability to have many people modifying the same collection of files knowing that conflicting modifications can be detected and resolved. • History: the ability to attach historical data to your data, such as explanatory comments about the intention behind each change to it. Even for a programmer working solo, change histories are an important aid to memory; for a multi-person project, they are a vitally important form of communication among developers. ## Supported Version Control Systems VC currently works with many different version control systems, which it refers to as back ends: • SCCS was the first version control system ever built, and was long ago superseded by more advanced ones. VC compensates for certain features missing in SCCS (e.g., tag names for releases) by implementing them itself. Other VC features, such as multiple branches, are unavailable. Since SCCS is non-free, we recommend avoiding it. • CSSC is a free replacement for SCCS. You should use CSSC only if, for some reason, you cannot use a more recent and better-designed version control system. • RCS is the free version control system around which VC was initially built. It is relatively primitive: it cannot be used over the network, and works at the level of individual files. Almost everything you can do with RCS can be done through VC. • CVS is the free version control system that was, until recently (circa 2008), used by the majority of free software projects. Nowadays, it is slowly being superseded by newer systems. CVS allows concurrent multi-user development either locally or over the network. Unlike newer systems, it lacks support for atomic commits and file moving/renaming. VC supports all basic editing operations under CVS. • Subversion (svn) is a free version control system designed to be similar to CVS but without its problems (e.g., it supports atomic commits of filesets, and versioning of directories, symbolic links, meta-data, renames, copies, and deletes). • GNU Arch is one of the earliest decentralized version control systems (the other being Monotone). See VCS Concepts, for a description of decentralized version control systems. It is no longer under active development, and has been deprecated in favor of Bazaar. • Git is a decentralized version control system originally invented by Linus Torvalds to support development of Linux (his kernel). VC supports many common Git operations, but others, such as repository syncing, must be done from the command line. • Mercurial (hg) is a decentralized version control system broadly resembling Git. VC supports most Mercurial commands, with the exception of repository sync operations. • Bazaar (bzr) is a decentralized version control system that supports both repository-based and decentralized versioning. VC supports most basic editing operations under Bazaar. ## Concepts of Version Control When a file is under version control, we say that it is registered in the version control system. The system has a repository which stores both the file's present state and its change history—enough to reconstruct the current version or any earlier version. The repository also contains other information, such as log entries that describe the changes made to each file. The copy of a version-controlled file that you actually edit is called the work file. You can change each work file as you would an ordinary file. After you are done with a set of changes, you may commit (or check in) the changes; this records the changes in the repository, along with a descriptive log entry. A directory tree of work files is called a working tree. Each commit creates a new revision in the repository. The version control system keeps track of all past revisions and the changes that were made in each revision. Each revision is named by a revision ID, whose format depends on the version control system; in the simplest case, it is just an integer. To go beyond these basic concepts, you will need to understand three aspects in which version control systems differ. As explained in the next three sections, they can be lock-based or merge-based; file-based or changeset-based; and centralized or decentralized. VC handles all these modes of operation, but it cannot hide the differences. ## Merge-based vs. Lock-based Version Control A version control system typically has some mechanism to coordinate between users who want to change the same file. There are two ways to do this: merging and locking. In a version control system that uses merging, each user may modify a work file at any time. The system lets you merge your work file, which may contain changes that have not been committed, with the latest changes that others have committed. Older version control systems use a locking scheme instead. Here, work files are normally read-only. To edit a file, you ask the version control system to make it writable for you by locking it; only one user can lock a given file at any given time. This procedure is analogous to, but different from, the locking that Emacs uses to detect simultaneous editing of ordinary files (see Interlocking). When you commit your changes, that unlocks the file, and the work file becomes read-only again. Other users may then lock the file to make their own changes. Both locking and merging systems can have problems when multiple users try to modify the same file at the same time. Locking systems have lock conflicts; a user may try to check a file out and be unable to because it is locked. In merging systems, merge conflicts happen when you commit a change to a file that conflicts with a change committed by someone else after your checkout. Both kinds of conflict have to be resolved by human judgment and communication. Experience has shown that merging is superior to locking, both in convenience to developers and in minimizing the number and severity of conflicts that actually occur. SCCS always uses locking. RCS is lock-based by default but can be told to operate in a merging style. CVS and Subversion are merge-based by default but can be told to operate in a locking mode. Decentralized version control systems, such as GNU Arch, Git, and Mercurial, are exclusively merging-based. VC mode supports both locking and merging version control. The terms "commit" and "update" are used in newer version control systems; older lock-based systems use the terms "check in" and "check out". VC hides the differences between them as much as possible. ## Changeset-based vs. File-based Version Control Systems On SCCS, RCS, CVS, and other early version control systems, version control operations are file-based: each file has its own comment and revision history separate from that of all other files. Newer systems, beginning with Subversion, are changeset-based: a commit may include changes to several files, and the entire set of changes is handled as a unit. Any comment associated with the change does not belong to a single file, but to the changeset itself. Changeset-based version control is more flexible and powerful than file-based version control; usually, when a change to multiple files has to be reversed, it's good to be able to easily identify and remove all of it. ## Decentralized vs. Centralized Repositories Early version control systems were designed around a centralized model in which each project has only one repository used by all developers. SCCS, RCS, CVS, and Subversion share this kind of model. One of its drawbacks is that the repository is a choke point for reliability and efficiency. GNU Arch pioneered the concept of distributed or decentralized version control, later implemented in Git, Mercurial, and Bazaar. A project may have different repositories, and these systems support a sort of super-merge between repositories that tries to reconcile their change histories. In effect, there is one repository for each developer, and repository merges take the place of commit operations. VC helps you manage the traffic between your personal workfiles and a repository. Whether the repository is a single master, or one of a network of peer repositories, is not something VC has to care about. ## Types of Log File Projects that use a version control system can have two types of log for changes. One is the log maintained by the version control system: each time you commit a change, you fill out a log entry for the change (see Log Buffer). This is called the version control log. The other kind of log is the file ChangeLog (see Change Log). It provides a chronological record of all changes to a large portion of a program—typically one directory and its subdirectories. A small program would use one ChangeLog file; a large program may have a ChangeLog file in each major directory. Programmers have used change logs since long before version control systems. Changeset-based version systems typically maintain a changeset-based modification log for the entire system, which makes change log files somewhat redundant. One advantage that they retain is that it is sometimes useful to be able to view the transaction history of a single directory separately from those of other directories. A project maintained with version control can use just the version control log, or it can use both kinds of logs. It can handle some files one way and some files the other way. Each project has its policy, which you should follow. When the policy is to use both, you typically want to write an entry for each change just once, then put it into both logs. You can write the entry in ChangeLog, then copy it to the log buffer with C-c C-a when committing the change (see Log Buffer). Or you can write the entry in the log buffer while committing the change, and later use the C-x v a command to copy it to ChangeLog (see Change Logs and VC). ## Version Control and the Mode Line When you visit a file that is under version control, Emacs indicates this on the mode line. For example, 'Bzr-1223' says that Bazaar is used for that file, and the current revision ID is 1223. The character between the back-end name and the revision ID indicates the version control status of the work file. In a merge-based version control system, a '-' character indicates that the work file is unmodified, and ':' indicates that it has been modified. '!' indicates that the file contains conflicts as result of a recent merge operation (see Merging), or that the file was removed from the version control. Finally, '?' means that the file is under version control, but is missing from the working tree. In a lock-based system, '-' indicates an unlocked file, and ':' a locked file; if the file is locked by another user (for instance, 'jim'), that is displayed as 'RCS:jim:1.3'. '@' means that the file was locally added, but not yet committed to the master repository. On a graphical display, you can move the mouse over this mode line indicator to pop up a "tool-tip", which displays a more verbose description of the version control status. Pressing Mouse-1 over the indicator pops up a menu of VC commands, identical to 'Tools / Version Control' on the menu bar. When Auto Revert mode (see Reverting) reverts a buffer that is under version control, it updates the version control information in the mode line. However, Auto Revert mode may not properly update this information if the version control status changes without changes to the work file, from outside the current Emacs session. If you set auto-revert-check-vc-info to t, Auto Revert mode updates the version control status information every auto-revert-interval seconds, even if the work file itself is unchanged. The resulting CPU usage depends on the version control system, but is usually not excessive. ## Basic Editing under Version Control Most VC commands operate on VC filesets. A VC fileset is a collection of one or more files that a VC operation acts on. When you type VC commands in a buffer visiting a version-controlled file, the VC fileset is that one file. When you type them in a VC Directory buffer, and some files in it are marked, the VC fileset consists of the marked files (see VC Directory Mode). On modern changeset-based version control systems (see VCS Changesets), VC commands handle multi-file VC filesets as a group. For example, committing a multi-file VC fileset generates a single revision, containing the changes to all those files. On older file-based version control systems like CVS, each file in a multi-file VC fileset is handled individually; for example, a commit generates one revision for each changed file.  C-x v v Perform the next appropriate version control operation on the current VC fileset. The principal VC command is a multi-purpose command, C-x v v (vc-next-action), which performs the "most appropriate" action on the current VC fileset: either registering it with a version control system, or committing it, or unlocking it, or merging changes into it. The precise actions are described in detail in the following subsections. You can use C-x v v either in a file-visiting buffer or in a VC Directory buffer. Note that VC filesets are distinct from the "named filesets" used for viewing and visiting files in functional groups (see Filesets). Unlike named filesets, VC filesets are not named and don't persist across sessions. ## VC With A Merging VCS On a merging-based version control system (i.e., most modern ones; see VCS Merging), C-x v v does the following: • If there is more than one file in the VC fileset and the files have inconsistent version control statuses, signal an error. (Note, however, that a fileset is allowed to include both "newly-added" files and "modified" files; see Registering.) • If none of the files in the VC fileset are registered with a version control system, register the VC fileset, i.e., place it under version control. See Registering. If Emacs cannot find a system to register under, it prompts for a repository type, creates a new repository, and registers the VC fileset with it. • If every work file in the VC fileset is unchanged, do nothing. • If every work file in the VC fileset has been modified, commit the changes. To do this, Emacs pops up a *vc-log* buffer; type the desired log entry for the new revision, followed by C-c C-c to commit. See Log Buffer. If committing to a shared repository, the commit may fail if the repository that has been changed since your last update. In that case, you must perform an update before trying again. On a decentralized version control system, use C-x v + (see VC Pull) or C-x v m (see Merging). On a centralized version control system, type C-x v v again to merge in the repository changes. • Finally, if you are using a centralized version control system, check if each work file in the VC fileset is up-to-date. If any file has been changed in the repository, offer to update it. These rules also apply when you use RCS in its "non-locking" mode, except that changes are not automatically merged from the repository. Nothing informs you if another user has committed changes in the same file since you began editing it; when you commit your revision, his changes are removed (however, they remain in the repository and are thus not irrevocably lost). Therefore, you must verify that the current revision is unchanged before committing your changes. Also, locking is possible with RCS even in this mode: C-x v v with an unmodified file locks the file, just as it does with RCS in its normal locking mode (see VC With A Locking VCS). ## Basic Version Control with Locking On a locking-based version control system (such as SCCS, and RCS in its default mode), C-x v v does the following: • If there is more than one file in the VC fileset and the files have inconsistent version control statuses, signal an error. • If each file in the VC fileset is not registered with a version control system, register the VC fileset. See Registering. If Emacs cannot find a system to register under, it prompts for a repository type, creates a new repository, and registers the VC fileset with it. • If each file is registered and unlocked, lock it and make it writable, so that you can begin to edit it. • If each file is locked by you and contains changes, commit the changes. To do this, Emacs pops up a *vc-log* buffer; type the desired log entry for the new revision, followed by C-c C-c to commit (see Log Buffer). • If each file is locked by you, but you have not changed it, release the lock and make the file read-only again. • If each file is locked by another user, ask whether you want to "steal the lock". If you say yes, the file becomes locked by you, and a warning message is sent to the user who had formerly locked the file. These rules also apply when you use CVS in locking mode, except that CVS does not support stealing locks. ## Advanced Control in C-x v v When you give a prefix argument to vc-next-action (C-u C-x v v), it still performs the next logical version control operation, but accepts additional arguments to specify precisely how to do the operation. • You can specify the name of a version control system. This is useful if the fileset can be managed by more than one version control system, and Emacs fails to detect the correct one. • Otherwise, if using CVS or RCS, you can specify a revision ID. If the fileset is modified (or locked), this makes Emacs commit with that revision ID. You can create a new branch by supplying an appropriate revision ID (see Branches). If the fileset is unmodified (and unlocked), this checks the specified revision into the working tree. You can also specify a revision on another branch by giving its revision or branch ID (see Switching Branches). An empty argument (i.e., C-u C-x v v <RET>) checks out the latest ("head") revision on the current branch. This signals an error on a decentralized version control system. Those systems do not let you specify a revision IDs, nor do they use the concept of "checking out" individual files. ## Features of the Log Entry Buffer When you tell VC to commit a change, it pops up a buffer named *vc-log*. In this buffer, you should write a log entry describing the changes you have made (see Why Version Control?). After you are done, type C-c C-c (log-edit-done) to exit the buffer and commit the change, together with your log entry. The major mode for the *vc-log* buffer is Log Edit mode, a variant of Text mode (see Text Mode). On entering Log Edit mode, Emacs runs the hooks text-mode-hook and vc-log-mode-hook (see Hooks). In the *vc-log* buffer, you can write one or more header lines, specifying additional information to be supplied to the version control system. Each header line must occupy a single line at the top of the buffer; the first line that is not a header line is treated as the start of the log entry. For example, the following header line states that the present change was not written by you, but by another developer: Author: J. R. Hacker <[email protected]> Apart from the 'Author' header, Emacs recognizes the headers 'Date' (a manually-specified commit time) and 'Fixes' (a reference to a bug fixed by the change). Not all version control systems recognize all headers: Bazaar recognizes all three headers, while Git, Mercurial, and Monotone recognize only 'Author' and 'Date'. If you specify a header for a system that does not support it, the header is treated as part of the log entry. While in the *vc-log* buffer, the "current VC fileset" is considered to be the fileset that will be committed if you type C-c C-c. To view a list of the files in the VC fileset, type C-c C-f (log-edit-show-files). To view a diff of changes between the VC fileset and the version from which you started editing (see Old Revisions), type C-c C-d (log-edit-show-diff). If the VC fileset includes one or more ChangeLog files (see Change Log), type C-c C-a (log-edit-insert-changelog) to pull the relevant entries into the *vc-log* buffer. If the topmost item in each ChangeLog was made under your username on the current date, this command searches that item for entries matching the file(s) to be committed, and inserts them. If you are using CVS or RCS, see Change Logs and VC, for the opposite way of working—generating ChangeLog entries from the Log Edit buffer. To abort a commit, just don't type C-c C-c in that buffer. You can switch buffers and do other editing. As long as you don't try to make another commit, the entry you were editing remains in the *vc-log* buffer, and you can go back to that buffer at any time to complete the commit. You can also browse the history of previous log entries to duplicate a commit comment. This can be useful when you want to make several commits with similar comments. The commands M-n, M-p, M-s and M-r for doing this work just like the minibuffer history commands (see Minibuffer History), except that they are used outside the minibuffer. ## Registering a File for Version Control  C-x v i Register the visited file for version control. The command C-x v i (vc-register) registers each file in the current VC fileset, placing it under version control. This is essentially equivalent to the action of C-x v v on an unregistered VC fileset (see Basic VC Editing), except that if the VC fileset is already registered, C-x v i signals an error whereas C-x v v performs some other action. To register a file, Emacs must choose a version control system. For a multi-file VC fileset, the VC Directory buffer specifies the system to use (see VC Directory Mode). For a single-file VC fileset, if the file's directory already contains files registered in a version control system, or if the directory is part of a directory tree controlled by a version control system, Emacs chooses that system. In the event that more than one version control system is applicable, Emacs uses the one that appears first in the variable vc-handled-backends (see Customizing VC). If Emacs cannot find a version control system to register the file under, it prompts for a repository type, creates a new repository, and registers the file into that repository. On most version control systems, registering a file with C-x v i or C-x v v adds it to the "working tree" but not to the repository. Such files are labeled as 'added' in the VC Directory buffer, and show a revision ID of '@@' in the mode line. To make the registration take effect in the repository, you must perform a commit (see Basic VC Editing). Note that a single commit can include both file additions and edits to existing files. On a locking-based version control system (see VCS Merging), registering a file leaves it unlocked and read-only. Type C-x v v to start editing it. ## Examining and Comparing Old Revisions  C-x v = Compare the work files in the current VC fileset with the versions you started from (vc-diff). With a prefix argument, prompt for two revisions of the current VC fileset and compare them. You can also call this command from a Dired buffer (see Dired). M-x vc-ediff Like C-x v =, but using Ediff. C-x v D Compare the entire working tree to the revision you started from (vc-root-diff). With a prefix argument, prompt for two revisions and compare their trees. C-x v ~ Prompt for a revision of the current file, and visit it in a separate buffer (vc-revision-other-window). C-x v g Display an annotated version of the current file: for each line, show the latest revision in which it was modified (vc-annotate). C-x v = (vc-diff) displays a diff which compares each work file in the current VC fileset to the version(s) from which you started editing. The diff is displayed in another window, in a Diff mode buffer (see Diff Mode) named *vc-diff*. The usual Diff mode commands are available in this buffer. In particular, the g (revert-buffer) command performs the file comparison again, generating a new diff. To compare two arbitrary revisions of the current VC fileset, call vc-diff with a prefix argument: C-u C-x v =. This prompts for two revision IDs (see VCS Concepts), and displays a diff between those versions of the fileset. This will not work reliably for multi-file VC filesets, if the version control system is file-based rather than changeset-based (e.g., CVS), since then revision IDs for different files would not be related in any meaningful way. Instead of the revision ID, some version control systems let you specify revisions in other formats. For instance, under Bazaar you can enter 'date:yesterday' for the argument to C-u C-x v = (and related commands) to specify the first revision committed after yesterday. See the documentation of the version control system for details. If you invoke C-x v = or C-u C-x v = from a Dired buffer (see Dired), the file listed on the current line is treated as the current VC fileset. M-x vc-ediff works like C-x v =, except that it uses an Ediff session. C-x v D (vc-root-diff) is similar to C-x v =, but it displays the changes in the entire current working tree (i.e., the working tree containing the current VC fileset). If you invoke this command from a Dired buffer, it applies to the working tree containing the directory. You can customize the diff options that C-x v = and C-x v D use for generating diffs. The options used are taken from the first non-nil value amongst the variables vc-backend-diff-switches, vc-diff-switches, and diff-switches (see Comparing Files), in that order. Here, backend stands for the relevant version control system, e.g., bzr for Bazaar. Since nil means to check the next variable in the sequence, either of the first two may use the value t to mean no switches at all. Most of the vc-backend-diff-switches variables default to nil, but some default to t; these are for version control systems whose diff implementations do not accept common diff options, such as Subversion. To directly examine an older version of a file, visit the work file and type C-x v ~ revision <RET> (vc-revision-other-window). This retrieves the file version corresponding to revision, saves it to filename.~revision~, and visits it in a separate window. Many version control systems allow you to view files annotated with per-line revision information, by typing C-x v g (vc-annotate). This creates a new buffer (the "annotate buffer") displaying the file's text, with each line colored to show how old it is. Red text is new, blue is old, and intermediate colors indicate intermediate ages. By default, the color is scaled over the full range of ages, such that the oldest changes are blue, and the newest changes are red. When you give a prefix argument to this command, Emacs reads two arguments using the minibuffer: the revision to display and annotate (instead of the current file contents), and the time span in days the color range should cover. From the annotate buffer, these and other color scaling options are available from the 'VC-Annotate' menu. In this buffer, you can also use the following keys to browse the annotations of past revisions, view diffs, or view log entries:  p Annotate the previous revision, i.e., the revision before the one currently annotated. A numeric prefix argument is a repeat count, so C-u 10 p would take you back 10 revisions. n Annotate the next revision, i.e., the revision after the one currently annotated. A numeric prefix argument is a repeat count. j Annotate the revision indicated by the current line. a Annotate the revision before the one indicated by the current line. This is useful to see the state the file was in before the change on the current line was made. f Show in a buffer the file revision indicated by the current line. d Display the diff between the current line's revision and the previous revision. This is useful to see what the current line's revision actually changed in the file. D Display the diff between the current line's revision and the previous revision for all files in the changeset (for VC systems that support changesets). This is useful to see what the current line's revision actually changed in the tree. l Show the log of the current line's revision. This is useful to see the author's description of the changes in the revision on the current line. w Annotate the working revision–the one you are editing. If you used p and n to browse to other revisions, use this key to return to your working revision. v Toggle the annotation visibility. This is useful for looking just at the file contents without distraction from the annotations. ## VC Change Log  C-x v l Display the change history for the current fileset (vc-print-log). C-x v L Display the change history for the current repository (vc-print-root-log). C-x v I Display the changes that a pull operation will retrieve (vc-log-incoming). C-x v O Display the changes that will be sent by the next push operation (vc-log-outgoing). C-x v l (vc-print-log) displays a buffer named *vc-change-log*, showing the history of changes made to the current file, including who made the changes, the dates, and the log entry for each change (these are the same log entries you would enter via the *vc-log* buffer; see Log Buffer). Point is centered at the revision of the file currently being visited. With a prefix argument, the command prompts for the revision to center on, and the maximum number of revisions to display. If you call C-x v l from a VC Directory buffer (see VC Directory Mode) or a Dired buffer (see Dired), it applies to the file listed on the current line. C-x v L (vc-print-root-log) displays a *vc-change-log* buffer showing the history of the entire version-controlled directory tree (RCS, SCCS, and CVS do not support this feature). With a prefix argument, the command prompts for the maximum number of revisions to display. The C-x v L history is shown in a compact form, usually showing only the first line of each log entry. However, you can type <RET> (log-view-toggle-entry-display) in the *vc-change-log* buffer to reveal the entire log entry for the revision at point. A second <RET> hides it again. On a decentralized version control system, the C-x v I (vc-log-incoming) command displays a log buffer showing the changes that will be applied, the next time you run the version control system's "pull" command to get new revisions from another repository (see VC Pull). This other repository is the default one from which changes are pulled, as defined by the version control system; with a prefix argument, vc-log-incoming prompts for a specific repository. Similarly, C-x v O (vc-log-outgoing) shows the changes that will be sent to another repository, the next time you run the "push" command; with a prefix argument, it prompts for a specific destination repository. In the *vc-change-log* buffer, you can use the following keys to move between the logs of revisions and of files, and to examine and compare past revisions (see Old Revisions):  p Move to the previous revision entry. (Revision entries in the log buffer are usually in reverse-chronological order, so the previous revision-item usually corresponds to a newer revision.) A numeric prefix argument is a repeat count. n Move to the next revision entry. A numeric prefix argument is a repeat count. P Move to the log of the previous file, if showing logs for a multi-file VC fileset. Otherwise, just move to the beginning of the log. A numeric prefix argument is a repeat count. N Move to the log of the next file, if showing logs for a multi-file VC fileset. A numeric prefix argument is a repeat count. a Annotate the revision on the current line (see Old Revisions). e Modify the change comment displayed at point. Note that not all VC systems support modifying change comments. f Visit the revision indicated at the current line. d Display a diff between the revision at point and the next earlier revision, for the specific file. D Display the changeset diff between the revision at point and the next earlier revision. This shows the changes to all files made in that revision. In a compact-style log buffer (e.g., the one created by C-x v L), toggle between showing and hiding the full log entry for the revision at point. Because fetching many log entries can be slow, the *vc-change-log* buffer displays no more than 2000 revisions by default. The variable vc-log-show-limit specifies this limit; if you set the value to zero, that removes the limit. You can also increase the number of revisions shown in an existing *vc-change-log* buffer by clicking on the 'Show 2X entries' or 'Show unlimited entries' buttons at the end of the buffer. However, RCS, SCCS, and CVS do not support this feature. ## Undoing Version Control Actions  C-x v u Revert the work file(s) in the current VC fileset to the last revision (vc-revert). If you want to discard all the changes you have made to the current VC fileset, type C-x v u (vc-revert-buffer). This shows you a diff between the work file(s) and the revision from which you started editing, and asks for confirmation for discarding the changes. If you agree, the fileset is reverted. If you don't want C-x v u to show a diff, set the variable vc-revert-show-diff to nil (you can still view the diff directly with C-x v =; see Old Revisions). Note that C-x v u cannot be reversed with the usual undo commands (see Undo), so use it with care. On locking-based version control systems, C-x v u leaves files unlocked; you must lock again to resume editing. You can also use C-x v u to unlock a file if you lock it and then decide not to change it. ## VC Directory Mode Directory buffer is a specialized buffer for viewing the version control statuses of the files in a directory tree, and performing version control operations on those files. In particular, it is used to specify multi-file VC filesets for commands like C-x v v to act on (see VC Directory Commands). To use the VC Directory buffer, type C-x v d (vc-dir). This reads a directory name using the minibuffer, and switches to a VC Directory buffer for that directory. By default, the buffer is named *vc-dir*. Its contents are described in VC Directory Buffer. The vc-dir command automatically detects the version control system to be used in the specified directory. In the event that more than one system is being used in the directory, you should invoke the command with a prefix argument, C-u C-x v d; this prompts for the version control system which the VC Directory buffer should use. In addition to the VC Directory buffer, Emacs has a similar facility called PCL-CVS that is specialized for CVS. • Buffer: What the buffer looks like and means. • Commands: Commands to use in a VC directory buffer. ## The VC Directory Buffer The VC Directory buffer contains a list of version-controlled files and their version control statuses. It lists files in the current directory (the one specified when you called C-x v d) and its subdirectories, but only those with a "noteworthy" status. Files that are up-to-date (i.e., the same as in the repository) are omitted. If all the files in a subdirectory are up-to-date, the subdirectory is not listed either. As an exception, if a file has become up-to-date as a direct result of a VC command, it is listed. Here is an example of a VC Directory buffer listing:  ./ edited configure.ac * added README unregistered temp.txt src/ * edited src/main.c  Two work files have been modified but not committed: configure.ac in the current directory, and foo.c in the src/ subdirectory. The file named README has been added but is not yet committed, while temp.txt is not under version control (see Registering). The '*' characters next to the entries for README and src/main.c indicate that the user has marked out these files as the current VC fileset (see VC Directory Commands). The above example is typical for a decentralized version control system like Bazaar, Git, or Mercurial. Other systems can show other statuses. For instance, CVS shows the 'needs-update' status if the repository has changes that have not been applied to the work file. RCS and SCCS show the name of the user locking a file as its status. On CVS and Subversion, the vc-dir command normally contacts the repository, which may be on a remote machine, to check for updates. If you change the variable vc-stay-local or vc-cvs-stay-local (for CVS) to nil (see Options), then Emacs avoids contacting a remote repository when generating the VC Directory buffer (it will still contact it when necessary, e.g., when doing a commit). This may be desirable if you are working offline or the network is slow. The VC Directory buffer omits subdirectories listed in the variable vc-directory-exclusion-list. Its default value contains directories that are used internally by version control systems. ## VC Directory Commands Emacs provides several commands for navigating the VC Directory buffer, and for "marking" files as belonging to the current VC fileset.  n, Move point to the next entry (vc-dir-next-line). p Move point to the previous entry (vc-dir-previous-line). Move to the next directory entry (vc-dir-next-directory). S- Move to the previous directory entry (vc-dir-previous-directory). , f Visit the file or directory listed on the current line (vc-dir-find-file). o Visit the file or directory on the current line, in a separate window (vc-dir-find-file-other-window). m Mark the file or directory on the current line (vc-dir-mark), putting it in the current VC fileset. If the region is active, mark all files in the region. A file cannot be marked with this command if it is already in a marked directory, or one of its subdirectories. Similarly, a directory cannot be marked with this command if any file in its tree is marked. M If point is on a file entry, mark all files with the same status; if point is on a directory entry, mark all files in that directory tree (vc-dir-mark-all-files). With a prefix argument, mark all listed files and directories. q Quit the VC Directory buffer, and bury it (quit-window). u Unmark the file or directory on the current line. If the region is active, unmark all the files in the region (vc-dir-unmark). U If point is on a file entry, unmark all files with the same status; if point is on a directory entry, unmark all files in that directory tree (vc-dir-unmark-all-files). With a prefix argument, unmark all files and directories. x Hide files with 'up-to-date' status (vc-dir-hide-up-to-date). While in the VC Directory buffer, all the files that you mark with m (vc-dir-mark) or M (vc-dir-mark) are in the current VC fileset. If you mark a directory entry with m, all the listed files in that directory tree are in the current VC fileset. The files and directories that belong to the current VC fileset are indicated with a '*' character in the VC Directory buffer, next to their VC status. In this way, you can set up a multi-file VC fileset to be acted on by VC commands like C-x v v (see Basic VC Editing), C-x v = (see Old Revisions), and C-x v u (see VC Undo). The VC Directory buffer also defines some single-key shortcuts for VC commands with the C-x v prefix: =, +, l, i, and v. For example, you can commit a set of edited files by opening a VC Directory buffer, where the files are listed with the 'edited' status; marking the files; and typing v or C-x v v (vc-next-action). If the version control system is changeset-based, Emacs will commit the files in a single revision. While in the VC Directory buffer, you can also perform search and replace on the current VC fileset, with the following commands:  S Search the fileset (vc-dir-search). Q Do a regular expression query replace on the fileset (vc-dir-query-replace-regexp). M-s a C-s Do an incremental search on the fileset (vc-dir-isearch). M-s a C-M-s Do an incremental regular expression search on the fileset (vc-dir-isearch-regexp). Apart from acting on multiple files, these commands behave much like their single-buffer counterparts (see Search). The above commands are also available via the menu bar, and via a context menu invoked by Mouse-2. Furthermore, some VC backends use the menu to provide extra backend-specific commands. For example, Git and Bazaar allow you to manipulate stashes and shelves (where are a way to temporarily put aside uncommitted changes, and bring them back at a later time). ## Version Control Branches One use of version control is to support multiple independent lines of development, which are called branches. Branches are used for maintaining separate "stable" and "development" versions of a program, and for developing unrelated features in isolation from one another. VC's support for branch operations is currently fairly limited. For decentralized version control systems, it provides commands for updating one branch with the contents of another, and for merging the changes made to two different branches (see Merging). For centralized version control systems, it supports checking out different branches and committing into new or different branches. ## Switching Between Branches The various version control systems differ in how branches are implemented, and these differences cannot be entirely concealed by VC. On some decentralized version control systems, including Bazaar and Mercurial in its normal mode of operation, each branch has its own working directory tree, so switching between branches just involves switching directories. On Git, switching between branches is done using the git branch command, which changes the contents of the working tree itself. On centralized version control systems, you can switch between branches by typing C-u C-x v v in an up-to-date work file (see Advanced C-x v v), and entering the revision ID for a revision on another branch. On CVS, for instance, revisions on the trunk (the main line of development) normally have IDs of the form 1.1, 1.2, 1.3, ..., while the first branch created from (say) revision 1.2 has revision IDs 1.2.1.1, 1.2.1.2, ..., the second branch created from revision 1.2 has revision IDs 1.2.2.1, 1.2.2.2, ..., and so forth. You can also specify the branch ID, which is a branch revision ID omitting its final component (e.g., 1.2.1), to switch to the latest revision on that branch. On a locking-based system, switching to a different branch also unlocks (write-protects) the working tree. Once you have switched to a branch, VC commands will apply to that branch until you switch away; for instance, any VC filesets that you commit will be committed to that specific branch. ## Pulling Changes Into A Branch  C-x v + On a decentralized version control system, update the current branch by "pulling in" changes from another location. On a centralized version control system, update the current VC fileset. On a decentralized version control system, the command C-x v + (vc-pull) updates the current branch and working tree. It is typically used to update a copy of a remote branch. If you supply a prefix argument, the command prompts for the exact version control command to use, which lets you specify where to pull changes from. Otherwise, it pulls from a default location determined by the version control system. Amongst decentralized version control systems, C-x v + is currently supported only by Bazaar, Git, and Mercurial. On Bazaar, it calls bzr pull for ordinary branches (to pull from a master branch into a mirroring branch), and bzr update for a bound branch (to pull from a central repository). On Git, it calls git pull to fetch changes from a remote repository and merge it into the current branch. On Mercurial, it calls hg pull -u to fetch changesets from the default remote repository and update the working directory. Prior to pulling, you can use C-x v I (vc-log-incoming) to view a log buffer of the changes to be applied. See VC Change Log. On a centralized version control system like CVS, C-x v + updates the current VC fileset from the repository. ## Merging Branches  C-x v m On a decentralized version control system, merge changes from another branch into the current one. On a centralized version control system, merge changes from another branch into the current VC fileset. While developing a branch, you may sometimes need to merge in changes that have already been made in another branch. This is not a trivial operation, as overlapping changes may have been made to the two branches. On a decentralized version control system, merging is done with the command C-x v m (vc-merge). On Bazaar, this prompts for the exact arguments to pass to bzr merge, offering a sensible default if possible. On Git, this prompts for the name of a branch to merge from, with completion (based on the branch names known to the current repository). The output from running the merge command is shown in a separate buffer. On a centralized version control system like CVS, C-x v m prompts for a branch ID, or a pair of revision IDs (see Switching Branches); then it finds the changes from that branch, or the changes between the two revisions you specified, and merges those changes into the current VC fileset. If you just type <RET>, Emacs merges any changes that were made on the same branch since you checked the file out. Immediately after performing a merge, only the working tree is modified, and you can review the changes produced by the merge with C-x v D and related commands (see Old Revisions). If the two branches contained overlapping changes, merging produces a conflict; a warning appears in the output of the merge command, and conflict markers are inserted into each affected work file, surrounding the two sets of conflicting changes. You must then resolve the conflict by editing the conflicted files. Once you are done, the modified files must be committed in the usual way for the merge to take effect (see Basic VC Editing). ## Creating New Branches On centralized version control systems like CVS, Emacs supports creating new branches as part of a commit operation. When committing a modified VC fileset, type C-u C-x v v (vc-next-action with a prefix argument; see Advanced C-x v v/). Then Emacs prompts for a revision ID for the new revision. You should specify a suitable branch ID for a branch starting at the current revision. For example, if the current revision is 2.5, the branch ID should be 2.5.1, 2.5.2, and so on, depending on the number of existing branches at that point. To create a new branch at an older revision (one that is no longer the head of a branch), first select that revision (see Switching Branches). Your procedure will then differ depending on whether you are using a locking or merging-based VCS. On a locking VCS, you will need to lock the old revision branch with C-x v v. You'll be asked to confirm, when you lock the old revision, that you really mean to create a new branch—if you say no, you'll be offered a chance to lock the latest revision instead. On a merging-based VCS you will skip this step. Then make your changes and type C-x v v again to commit a new revision. This creates a new branch starting from the selected revision. After the branch is created, subsequent commits create new revisions on that branch. To leave the branch, you must explicitly select a different revision with C-u C-x v v. ## Miscellaneous Commands and Features of VC This section explains the less-frequently-used features of VC. ## Change Logs and VC If you use RCS or CVS for a program with a ChangeLog file (see Change Log), you can generate change log entries from the version control log entries of previous commits. Note that this only works with RCS or CVS. This procedure would be particularly incorrect on a modern changeset-based version control system, where changes to the ChangeLog file would normally be committed as part of a changeset. In that case, you should write the change log entries first, then pull them into the '*vc-log*' buffer when you commit (see Log Buffer).  C-x v a Visit the current directory's ChangeLog file and, for registered files in that directory, create new entries for versions committed since the most recent change log entry (vc-update-change-log). C-u C-x v a As above, but only find entries for the current buffer's file. For example, suppose the first line of ChangeLog is dated 1999-04-10, and that the only check-in since then was by Nathaniel Bowditch to rcs2log on 1999-05-22 with log entry 'Ignore log messages that start with #'.'. Then C-x v a inserts this ChangeLog entry: 1999-05-22 Nathaniel Bowditch <[email protected]> * rcs2log: Ignore log messages that start with #'.  If the version control log entry specifies a function name (in parenthesis at the beginning of a line), that is reflected in the ChangeLog entry. For example, if a log entry for vc.el is '(vc-do-command): Check call-process status.', the ChangeLog entry is: 1999-05-06 Nathaniel Bowditch <[email protected]> * vc.el (vc-do-command): Check call-process status. ` When C-x v a adds several change log entries at once, it groups related log entries together if they all are checked in by the same author at nearly the same time. If the log entries for several such files all have the same text, it coalesces them into a single entry. ## Deleting and Renaming Version-Controlled Files  M-x vc-delete-file Prompt for a file name, delete the file from the working tree, and schedule the deletion for committing. M-x vc-rename-file Prompt for two file names, VAR and OLD, rename them in the working tree, and schedule the renaming for committing. If you wish to delete a version-controlled file, use the command M-x vc-delete-file. This prompts for the file name, and deletes it via the version control system. The file is removed from the working tree, and in the VC Directory buffer (see VC Directory Mode), it is displayed with the 'removed' status. When you commit it, the deletion takes effect in the repository. To rename a version-controlled file, type M-x vc-rename-file. This prompts for two arguments: the name of the file you wish to rename, and the new name; then it performs the renaming via the version control system. The renaming takes effect immediately in the working tree, and takes effect in the repository when you commit the renamed file. On modern version control systems that have built-in support for renaming, the renamed file retains the full change history of the original file. On CVS and older version control systems, the vc-rename-file command actually works by creating a copy of the old file under the new name, registering it, and deleting the old file. In this case, the change history is not preserved. ## Revision Tags Most version control systems allow you to apply a revision tag to a specific version of a version-controlled tree. On modern changeset-based version control systems, a revision tag is a symbolic name for a particular revision. On older file-based systems like CVS, each tag is added to the entire set of version-controlled files, allowing them to be handled as a unit. Revision tags are commonly used to identify releases that are distributed to users. There are two basic commands for tags; one makes a tag with a given name, the other retrieves a named tag.  C-x v s name Define the working revision of every registered file in or under the current directory as a tag named name (vc-create-tag). C-x v r name For all registered files at or below the current directory level, retrieve the tagged revision name. This command will switch to a branch if name is a branch name and your VCS distinguishes branches from tags. (vc-retrieve-tag). This command reports an error if any files are locked at or below the current directory, without changing anything; this is to avoid overwriting work in progress. You can give a tag or branch name as an argument to C-x v = or C-x v ~ (see Old Revisions). Thus, you can use it to compare a tagged version against the current files, or two tagged versions against each other. On SCCS, VC implements tags itself; these tags are visible only through VC. Most later systems (including CVS, Subversion, bzr, git, and hg) have a native tag facility, and VC uses it where available; those tags will be visible even when you bypass VC. In a file-oriented VCS, when you rename a registered file you need to rename its master along with it; the command vc-rename-file will do this automatically. If you are using SCCS, you must also update the records of the tag, to mention the file by its new name (vc-rename-file does this, too). An old tag that refers to a master file that no longer exists under the recorded name is invalid; VC can no longer retrieve it. It would be beyond the scope of this manual to explain enough about RCS and SCCS to explain how to update the tags by hand. Using vc-rename-file makes the tag remain valid for retrieval, but it does not solve all problems. For example, some of the files in your program probably refer to others by name. At the very least, the makefile probably mentions the file that you renamed. If you retrieve an old tag, the renamed file is retrieved under its new name, which is not the name that the makefile expects. So the program won't really work as retrieved. ## Inserting Version Control Headers On Subversion, CVS, RCS, and SCCS, you can put certain special strings called version headers into a work file. When the file is committed, the version control system automatically puts the revision number, the name of the user who made the commit, and other relevant information into the version header. VC does not normally use the information in the version headers. As an exception, when using RCS, Emacs uses the version header, if there is one, to determine the file version, since it is often more reliable than the RCS master file. To inhibit using the version header this way, change the variable vc-consult-headers to nil. To insert a suitable header string into the current buffer, type C-x v h (vc-insert-headers). This command works only on Subversion, CVS, RCS, and SCCS. The variable vc-backend-header contains the list of keywords to insert into the version header; for instance, CVS uses vc-cvs-header, whose default value is '("\$Id\\$"). (The extra backslashes prevent the string constant from being interpreted as a header, if the Emacs Lisp file defining it is maintained with version control.) The C-x v h command inserts each keyword in the list on a new line at point, surrounded by tabs, and inside comment delimiters if necessary.

The variable vc-static-header-alist specifies further strings to add based on the name of the buffer. Its value should be a list of elements of the form (regexp . format). Whenever regexp matches the buffer name, format is also inserted as part of the version header. A '%s' in format is replaced with the file's version control type.

## Customizing VC

The variable vc-handled-backends determines w