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Like most users, I have a bunch of aliases set up to give a default set of flags for frequently used programs. For instance,

alias vim='vim -X'
alias grep='grep -E'
alias ls='ls -G'

The problem is that if I want to use which to see where my vim/grep/ls/etc is coming from, the alias gets in the way:

$ which vim
vim: aliased to vim -X

This is useful output, but not what I'm looking for in this case; I know vim is aliased to vim -X but I want to know where that vim is coming from.

Short of temporarily un-defining the alias just so I can use which on it, is there an easy way to have which 'unwrap' the alias and run itself on that?

Edit: It seems that which is a shell-builtin with different behaviors across different shells. In Bash, SiegeX's suggestion of the --skip-alias flag works; however, I'm on Zsh. Does something similar exist there?

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3 Answers 3

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which is actually a bad way to do things like this, as it makes guesses about your environment based on $SHELL and the startup files (it thinks) that shell uses; not only does it sometimes guess wrong, but you can't generally tell it to behave differently. (which on my Ubuntu 10.10 doesn't understand --skip-alias as mentioned by @SiegeX, for example.) type uses the current shell environment instead of poking at your config files, and can be told to ignore parts of that environment, so it shows you what will actually happen instead of what would happen in a reconstruction of your default shell.

In this case, type -P will bypass any aliases or functions:

$ type -P vim
/usr/bin/vim

You can also ask it to peel off all the layers, one at a time, and show you what it would find:

$ type -a vim
vim is aliased to `vim -X'
vim is /usr/bin/vim

(Expanding on this from the comments:)

The problem with which is that it's usually an external program instead of a shell built-in, which means it can't see your aliases or functions and has to try to reconstruct them from the shell's startup/config files. (If it's a shell built-in, as it is in zsh but apparently not bash, it is more likely to use the shell's environment and do the right thing.)

type is a POSIX-compliant command which is required to behave as if it were a built-in (that is, it must use the environment of the shell it's invoked from including local aliases and functions), so it usually is a built-in.

It isn't generally found in csh/tcsh, although in most modern versions of those which is a shell builtin and does the right thing; sometimes the built-in is what instead, and sometimes there's no good way to see the current shell's environment from csh/tcsh at all.

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Thanks! This is something very useful to add to my bag of tricks. I especially like that type -a seems to return all instances on your $PATH, not just the first one. I think I'll alias which to type :) –  Adrian Petrescu Apr 2 '11 at 20:49
    
type appears to be a bash builtin. Does this work on other shells? –  Faheem Mitha Apr 2 '11 at 20:55
    
type is part of POSIX, and derived from the original System V shell. It won't work on csh/tcsh; some versions of those have a what builtin, others may have a built-in version of which that behaves like type instead of like the standalone which (the stand-alone-ness is why it has to guess, btw; built-in versions are more likely to do the right thing, as it has to be built in to see what aliases and functions you have). –  geekosaur Apr 2 '11 at 20:59
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@ geekosaur: Thanks. If type is part of the POSIX standard then that is the way to go. To answer my question, type works on zsh too (on Debian). Why don't the distributions get rid of what and which if they aren't standardized and don't have extra functionality? –  Faheem Mitha Apr 2 '11 at 21:05
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@Faheem: re documentation, I'd start with info bash 'Bash builtins' on Linux, although you can also get it form the zsh reference manual. More officially, pubs.opengroup.org/onlinepubs/009695399/utilities/type.html (which I note doesn't actually spec -P or -a, or even -p which was the original form of -P, but does require that it use the current shell environment). –  geekosaur Apr 2 '11 at 21:23
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In bash:

type -P vim

In zsh:

type -p vim

In both:

/usr/bin/which vim

Or:

( unalias vim; type vim )
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Last one is cool. We can have an alias to do this. :) –  balki Jul 15 '11 at 6:23
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Try the following:

which --skip-alias vim
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Interesting! This works on Bash, but not on Zsh (I really didn't think this was going to be shell-dependent). This made me realize that which is actually a shell built-in and not a regular Unix utility as I had assumed. So I should edit my question and specify Zsh. Thanks for pointing this out to me! –  Adrian Petrescu Apr 2 '11 at 20:37
    
which is not a builtin, at least not on Debian. It is a shell script, and part of debianutils, so works on zsh. However, --skip-alias is not an option the which on Debian. Are there different varieties of which floating around? This does not apppear to be a standardized command. –  Faheem Mitha Apr 2 '11 at 21:01
    
@Faheem Mitha: It is a zsh builtin. See man zshbuiltins. which [ -wpams ] name ... Equivalent to whence -c. –  Mikel Apr 2 '11 at 22:03
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