A builtin (or builtin command, or shell builtin) is a command or function that is part of the shell itself. The command is "built-in" to the shell program — no external program is necessary to run the command, and a new process does not need to be created.
Builtin commands are available in most shells, including:
- The Windows command prompt
- Windows PowerShell
- Bash, the default shell of the Windows Subsystem for Linux and most Linux operating systems.
Tip: In bash, and in the Windows command prompt, you can display a list of builtin commands with the command help.