which —
locate a program file in the user's path
The which utility takes a list of command names and
searches the path for each executable file that would be run had these
commands actually been invoked.
The following options are available:
-a- List all instances of executables found (instead of just the first one of
each).
-s- No output, just return 0 if all of the executables are found, or 1 if some
were not found.
Some shells may provide a builtin which
command which is similar or identical to this utility. Consult the
builtin(1) manual page.
The which command first appeared in
FreeBSD 2.1.
The which utility was originally written in Perl and was
contributed by Wolfram Schneider
<wosch@FreeBSD.org>.
The current version of which was rewritten in C by
Daniel Papasian
<dpapasia@andrew.cmu.edu>.