which/whereis differences

"How about learning about whereis and which using whatis?

$ whatis which
which (1) - shows the full path of (shell) commands

$ whatis whereis
whereis (1) - locate the binary, source, and manual page files for a command

Basically, whereis searches for ""possibly useful"" files, while which only searches for executables.

I rarely use whereis. On the other hand, which is very useful, specially in scripts. which is the answer for the following question: Where does this command come from?

$ which ls
/bin/ls

$ whereis ls
ls: /bin/ls /usr/share/man/man1p/ls.1p.bz2 /usr/share/man/man1/ls.1.bz2"

"Quoting their man pages :

whereis :

whereis locates source/binary and
manuals sections for specified files.

For instance :

$ whereis php
php: /usr/bin/php /usr/share/php /usr/share/man/man1/php.1.gz

ie, the ""php"" executable, and some other stuff (like man pages).

and which :

which returns the pathnames of the
files which would be executed in the
current environment

For instance :

$ which php
/usr/bin/php

ie, only the ""php"" executable."