The command is available in Unix and Unix-like systems, the AROS shell,[3] for FreeDOS[4] and for Microsoft Windows.

It does this by searching for an executable or script in the directories listed in the environment variable PATH.

[6] Carlo Wood developed the GNU implementation used in most Linux-based operating systems.

The current version of which was rewritten by Daniel Papasian using the C programming language.

The command is available as a separate package for Microsoft Windows as part of the GnuWin32 project[1] and the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.