permet de connaitre le chemin d'installation d'une commande.
exemple :

$which docker
/usr/bin/docker

Usage: /usr/bin/which [options] [–] COMMAND […] Write the full path of COMMAND(s) to standard output.

--version, -[vV] Print version and exit successfully.
--help,          Print this help and exit successfully.
--skip-dot       Skip directories in PATH that start with a dot.
--skip-tilde     Skip directories in PATH that start with a tilde.
--show-dot       Don't expand a dot to current directory in output.
--show-tilde     Output a tilde for HOME directory for non-root.
--tty-only       Stop processing options on the right if not on tty.
--all, -a        Print all matches in PATH, not just the first
--read-alias, -i Read list of aliases from stdin.
--skip-alias     Ignore option --read-alias; don't read stdin.
--read-functions Read shell functions from stdin.
--skip-functions Ignore option --read-functions; don't read stdin.

Recommended use is to write the output of (alias; declare -f) to standard input, so that which can show aliases and shell functions. See which(1) for examples.

If the options –read-alias and/or –read-functions are specified then the output can be a full alias or function definition, optionally followed by the full path of each command used inside of those.

Report bugs to which-bugs@gnu.org.