Manual Pages  — WHICH

Some shells may provide a builtin which command which is similar or identical to this utility. Consult the builtin(1) manual page.

$ /usr/bin/which ls cp
/bin/ls
/bin/cp

Same as above with a specific PATH and showing all occurrences:

$ PATH=/bin:/rescue /usr/bin/which -a ls cp
/bin/ls
/rescue/ls
/bin/cp
/rescue/cp

which will show duplicates if the same executable is found more than once:

$ PATH=/bin:/bin /usr/bin/which -a ls
/bin/ls
/bin/ls

Do not show output. Just exit with an appropriate return code:

$ /usr/bin/which -s ls cp
$ echo $?
0

$ /usr/bin/which -s fakecommand
$ echo $?
1