Linux and Unix join command
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The join command forms, on the standard output, a join of the two relations specified by the lines of file1 and file2.
join [-a filenumber | -v filenumber ] [ -1 fieldnumber ] [ -2 fieldnumber ] [ -o list ] [ -e string ] [ -t char ] file1 file2
join [ -a filenumber ] [ -j fieldnumber ] [-j1 fieldnumber ] [ -j2 fieldnumber ] [ -o list ] [-e string ] [ -t char ] file1 file2
| -a filenumber | In addition to the normal output, produce a line for each unpairable line in file filenumber, where filenumber is 1 or 2. If both -a 1 and -a 2 are specified, all unpairable lines will be output. |
| -v filenumber | Instead of the default output, produce a line only for each unpairable line in filenumber, where filenumber is 1 or 2. If both -v 1 and -v 2 are specified, all unpairable lines will be output. |
| -l fieldnumber | Join on the fieldnumberth field of file 1 . Fields are decimal integers starting with 1. |
| -2 fieldnumber | Join on the fieldnumberth field of file 2. Fields are decimal integers starting with 1. |
| -j fieldnumber | Equivalent to -1fieldnumber -2fieldnumber. |
| -j1 fieldnumber | Equivalent to -1fieldnumber. |
| -j2 fieldnumber | Equivalent to -2fieldnumber Fields are numbered starting with 1. |
| -o list | Each output line includes the fields specified in list. Fields selected by list that do not appear in the input will be treated as empty output fields. (See the -e option.) Each element of which has the either the form filenumber.fieldnumber, or 0, which represents the join field. The common field is not printed unless specifically requested. |
| -e string | Replace empty output fields with string. |
| -t char | Use character char as a separator. Every appearance of char in a line is significant. The character char is used as the field separator for both input and output. With this option specified, the collating term should be the same as sort without the -b option. |
| file1 file2 | File name or directory and file name of the files being joined |