which

which [-a] command...

which searches for executables in the directories listed in the PATH environment variable and prints the path of the first match found.This is useful for determining which version of a command will be executed when multiple versions exist, or for confirming a command is installed and in your PATH.With -a, all matches are shown, revealing if multiple versions exist in different PATH directories. The first listed is the one that would be executed.

-a, --all

Print all matching executables in PATH, not just first

Which only searches PATH; it doesn't show shell builtins, aliases, or functions. Use type in bash or whence in zsh for comprehensive command lookup.Some systems have different which implementations with varying options. The -a flag is common but not universal.If a command isn't found, which typically exits with status 1 and produces no output (or an error message depending on implementation).

type(1), whereis(1), command(1), hash(1)