Re: [MLUG] which command in bash and elsewhere

[Mike Miller <EMAIL:PROTECTED>]

On Sat, 3 Nov 2007, Jonathan King wrote:

> On 11/3/07, Mike Miller <EMAIL:PROTECTED> wrote:
> > Tell us if you remember because that was a good one.  In tcsh, which I am
> > in the process of abandoning in favor of bash, you don't get that problem.
> > It always tells you correctly which command you are getting - alias,
> > builtin, etc.  I thought bash could be configured to do this correctly,
> > but maybe I'm wrong.
>
> I will check on that, but I am not optimistic.

Here's a really good clue:

http://www.unixguide.net/unix/bash/D1.shtml

The "type" command in bash, or "type -a" will do good things.  Example on 
with bash on Red Hat:

$ which which
alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde --read-functions'
        /usr/bin/which

$ which time
/usr/bin/time

$ type time
time is a shell keyword

$ type -a time
time is a shell keyword
time is /usr/bin/time

$ type which
which is aliased to `alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde --read-functions'

$ type -a which
which is aliased to `alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde --read-functions'
which is /usr/bin/which

$ type -a type
type is a shell builtin


> From "man type" which is really a man page for all bash built-ins:

type [-aftpP] name [name ...]
      With  no options, indicate how each name would be interpreted if
      used as a command name.  If the -t option is used, type prints a
      string  which  is  one  of alias, keyword, function, builtin, or
      file if  name  is  an  alias,  shell  reserved  word,  function,
      builtin,  or disk file, respectively.  If the name is not found,
      then nothing  is  printed,  and  an  exit  status  of  false  is
      returned.   If  the  -p  option is used, type either returns the
      name of the disk file that would be executed if name were speci-
      fied as a command name, or nothing if ``type -t name'' would not
      return file.  The -P option forces a PATH search for each  name,
      even if ``type -t name'' would not return file.  If a command is
      hashed, -p and -P print the hashed value,  not  necessarily  the
      file that appears first in PATH.  If the -a option is used, type
      prints all of the places that contain an executable named  name.
      This  includes  aliases  and  functions,  if  and only if the -p
      option is not also used.  The table of hashed  commands  is  not
      consulted  when  using -a.  The -f option suppresses shell func-
      tion lookup, as with the command builtin.  type returns true  if
      any of the arguments are found, false if none are found.


> > I can't find info on that right now.  "man which" does give some 
> > pointers on use of aliases for "which," but I don't know if that solves 
> > this problem.  "which" can definitely understand aliases but maybe not 
> > shell built-ins.
>
> If which isn't a built-in and I haven't lost all of my brain cells yet, 
> it just gets argc and argv, so it can't tell who called it, which means 
> it can't say to itself "ah; bash called me so I should point out that in 
> this case the user is likely to get a built-in for 'time'" If it were a 
> built-in, I think it could scan the names of the other built-ins and 
> figure this out.

You are probably right.  tcsh's "which" is built-in:

> which which
which: shell built-in command.

But the great thing is that bash's "type" command is built-in too and it 
does what we need.  All hail "type"!!

Mike

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