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What's the difference between which and whereis ?

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migrated from Sep 12 '09 at 22:41

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I'm sorry but on my 10.5.8 OS X system which and whereis always give the same results. Maybe this is a very OS X specific question, since I agree, a different result is expected. Maybe whereis does not comply to what it should do. At least the two examples (see below) are not working: whereis ls and whereis php always give the same result as which ... Can anybody confirm this? Does Snow Leopard behave the same? – Wolf Sep 12 '09 at 23:11
Yeah I know, thats why I asked this question. – Mk12 Sep 12 '09 at 23:25
up vote 57 down vote accepted

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

$  whereis ls
ls: /bin/ls /usr/share/man/man1p/ls.1p.bz2 /usr/share/man/man1/ls.1.bz2
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didn't know about whatis, thanks. – Mk12 Sep 12 '09 at 20:39
BTW, I'd remove the "osx" tag, as this question applies to all unix variants (including Linux, BSD, Mac OS X, ...) – Denilson Sá Sep 12 '09 at 20:44
changed to unix – Mk12 Sep 12 '09 at 23:24

whereis searches the standard *nix locations for a specified command.

which searches your user-specific PATH (which may include some of the locations whereis searches, and may not include others - it might also include some places that whereis doesn't search if you'd added to your PATH)

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What is *nix? – Mk12 Sep 12 '09 at 20:19
Unix, Linux etc. (Mac OS X belonging in the etc.) – Tom Sep 12 '09 at 20:23
Ohhh, haha, I always thought that stack overflow was censoring the U in unix whenever I saw that for some reason.. – Mk12 Sep 12 '09 at 22:19
Nope. Just a fairly common convention of creative wildcard use to refer to a family of similar operating systems. ;) – Dav Sep 12 '09 at 22:28

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

ie, only the "php" executable.

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Thanks for the examples. – Mk12 Sep 12 '09 at 20:21

which search for executables in the directories specified by the environment variable PATH. And if found out, the full pathname of this executable will be printed.

$ which ls
$ which ifconfig
$ # No output, because ifconfig only exist in root's PATH.

whereis search for executables, source files, and manual pages using a database built by system automatically.

$ whereis less
less: /bin/less /usr/bin/less /usr/bin/X11/less /usr/share/man/man1/less.1.gz

But it seems that whereis and locate don't use the same database. When I installed a software and then used whereis and locate immediately to search for this software. The result is that whereis could find out some files related to this software while locate couldn't. Do they really use different database? How the database work? --Well, how about refuse to be a pedant? :)

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