which is a Unix command used to identify the location of executables.
The command takes one or more arguments; for each of these arguments, it prints the full path of the executable to stdout that would have been executed if this argument had been entered into the shell. It does this by searching for an executable or script in the directories listed in the environment variable PATH. The which command is part of most Unix-like computers. It is also part of the C Shell, and is available as a separate package for Microsoft Windows or use the similar where.exe. The same functionality is available in MS-DOS, but not Windows, as the built-in TRUENAME command.
The functionality of the which command is similar to some implementations of the type command. POSIX specifies a command named command that also covers this functionality.