Testing for broken symlinks

Testing for broken symlinks

[Eric Mangold]

Hello,

Is there any way to test if a symlink is broken?

Trying to read from the file and catching the errors would suffice for me,  
but I'm curious if there is a more elegant method.

-Eric

Re: Testing for broken symlinks

[Peter Stephenson]

"Eric Mangold" wrote:
> Is there any way to test if a symlink is broken?

This will work:

  broken=(mylinktest(N-@))

  if (( ${#broken} )); then
    print mylinktest is a broken symbolic link
  else
    print mylinktest is not a symbolic link or is not broken
  fi

The basic point is that the command line argument mylinktest(N-@) is
removed unless mylinktest is a broken symbolic link, so you may have a
more efficient way to use the fact.

This works because - makes the shell follow symbolic links, while @
tells it to look only for symbolic links.  The only files that are
still resolved as symbolic links are those that are broken.  The N flag
then removes any failed glob, i.e. those not broken symbolic links.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070


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Re: Testing for broken symlinks

[Alexey Tourbin]

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On Wed, Apr 20, 2005 at 05:30:51PM +1000, Eric Mangold wrote:
> Is there any way to test if a symlink is broken?

if [ -L "$f" -a ! -e "$f" ]; then
	print "$f: broken symlink"
fi

$ ln -sf /asdf/zxcv .
$ test -L zxcv; echo $?
0
$ test -e zxcv; echo $?
1
$

The point is that lstat(2) succeeds but stat(2) fails on broken
symlinks.

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Re: Testing for broken symlinks

[Paul Lew]

>>>>> "Peter" == Peter Stephenson <pws@csr.com> writes:

    Eric>> Is there any way to test if a symlink is broken?

    Peter> This will work:

    Peter> broken=(mylinktest(N-@))

    Peter> if (( ${#broken} )); then
    Peter> print mylinktest is a broken symbolic link
    Peter> else
    Peter> print mylinktest is not a symbolic link or is not broken
    Peter> fi
    Peter> <snip>

A off-topic question, what ever happen to the old feature (some
eariler version of zsh) that displays an '&' at end of the bad symlink
when displaying filename completion lists?  e.g.,

   > touch foo1 foo2
   > ln -s not-exist foo3
   > ls foo<tab>
   foo1@   foo2@   foo3&

Re: Testing for broken symlinks

[Bart Schaefer]

On Apr 20, 10:20am, Paul Lew wrote:
}
} A off-topic question, what ever happen to the old feature (some
} eariler version of zsh) that displays an '&' at end of the bad symlink
} when displaying filename completion lists?

That must have been a *really* long time ago.  I find some commented-out
code in zsh-2.4/src/glob.c that lingers as far as 3.0.8's Src/glob.c,
but it's gone in 3.1.6 and later.  I cannot recall ever using a build of
zsh where that code was live.