finding symlinks without target

finding symlinks without target

[Sven Guckes]

Hi!

Problem:
Find (and print) all symbolic links without a target within the current dirtree.

Anyone hints?

Sven

Re: finding symlinks without target

[Bernd Eggink]

Sven Guckes wrote:
> 
> Hi!
> 
> Problem:
> Find (and print) all symbolic links without a target within the current dirtree.
> 
> Anyone hints?

Not too elegant, but it works:

   for d in *(@); do cat $d >/dev/null 2>&1 || print $d; done

Bernd

--
Bernd Eggink
Regionales Rechenzentrum der Uni Hamburg
eggink@rrz.uni-hamburg.de
http://www.rrz.uni-hamburg.de/eggink/BEggink.html

Re: finding symlinks without target

[Bruce Stephens]

guckes@math.fu-berlin.de said:
> Find (and print) all symbolic links without a target within the
> current dirtree. 

For big dirtrees, this is probably a job for find.  I can't see immediately 
how to do it in zsh.

**/*(@) gives the list of symbolic links, and **/*(-@) gives the list of 
symbolic links with targets which do exist.  Clearly, from this one can 
calculate the list of symbolic links which don't have existing targets, but 
there ought to be an easier way of doing it.

Re: finding symlinks without target

[Bart Schaefer]

On Jan 23,  3:47pm, Sven Guckes wrote:
} Subject: finding symlinks without target
}
} Find (and print) all symbolic links without a target within the current
} dirtree.

	file **/*(D@) | fgrep broken

(You may need to change the grep if you're not using GNU `file`.)

Oh, you want it all in zsh?

	for i in **/*(D@); [[ -f $i || -d $i ]] || echo $i

But I think the pipe to fgrep would be faster.  (Why isn't there a glob
qualifier to chase links?  **/*(@^.,@^/) would appear to be perfect, but
doesn't work.)

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Re: finding symlinks without target

[Bruce Stephens]

schaefer@brasslantern.com said:
> (Why isn't there a glob qualifier to chase links?  **/*(@^.,@^/) would
> appear to be perfect, but doesn't work.) 

There is, isn't there.  The - seems to be right, almost.  How about 
**/*(@-^.,@-^/)

Meaning those symbolic links whose referents aren't files or directories?  On 
the other hand, I'll bet this won't work, because the property of existence is 
probably required when globbing.  The question is a good one though: there 
ought to be a way of doing this, and it probably ought to be an example in the 
manual, because it's a common enough task, and it would be cool to have a 
one-liner for small trees.

Re: finding symlinks without target

[Peter Williams]

In message <980123080024.ZM16631@candle.brasslantern.com>, "Bart Schaefer" writ
es:
 >	file **/*(D@) | fgrep broken
 >
 >(You may need to change the grep if you're not using GNU `file`.)
 >
 >Oh, you want it all in zsh?
 >
 >	for i in **/*(D@); [[ -f $i || -d $i ]] || echo $i
 >
 >But I think the pipe to fgrep would be faster.  (Why isn't there a glob
 >qualifier to chase links?  **/*(@^.,@^/) would appear to be perfect, but
 >doesn't work.)

You could also implement it as a function with perl:

badsyms () {
    perl -e '{
        require "find.pl";
        sub wanted { !stat($_) && print("$name\n") }
        &find(@ARGV);
    }' $*
}

However, this seems a bit slower than M. Schaefer's solutions above.

Peter Williams <peter.williams@jpl.nasa.gov>

------------------ SITUATION: New Account Creation -------------------
ADMINISTRATIVE FASCIST:  Puts new account policy in motd.  Since
  people without accounts cannot read the motd, nobody ever fulfills
  the bureaucratic requirements; and so, no new accounts are ever
  created.
  -- Stephan Zielinski, "KNOW YOUR UNIX SYSTEM ADMINISTRATOR"

Re: zsh manual - more examples!

[Sven Guckes]

Quoting Bruce Stephens (B.Stephens@isode.com):
> [...] the property of existence is probably required when globbing.
> The question is a good one though: there ought to be a way of doing this,
> and it probably ought to be an example in the manual, because it's a common
> enough task, and it would be cool to have a one-liner for small trees.

Indeed - it seems such a basic problem that it ought be in the manual.
Btw, I find that manuals have way too far examples.  While I can understand
that not every example should be in a manual, the users would benefit A LOT
if the manual to their shell (read: ZShell) had more examples.

For now, I'll be adding more exmaples to my page about the zsh:

	http://www.math.fu-berlin.de/~guckes/zsh/

Sven

Re: finding symlinks without target

[Peter Williams]

In message <19980123154701.05885@math.fu-berlin.de>, Sven Guckes writes:
 >Hi!
 >
 >Problem:
 > Find (and print) all symbolic links without a target within the
 > current dirtree.

Why not implement it as a function with perl:

badsyms () {
    perl -e '{
        require "find.pl";
        sub wanted { !stat($_) && print("$name\n") }
        &find(@ARGV);
    }' $*
}

Peter Williams <peter.williams@jpl.nasa.gov>

------------------ SITUATION: New Account Creation -------------------
ADMINISTRATIVE FASCIST:  Puts new account policy in motd.  Since
  people without accounts cannot read the motd, nobody ever fulfills
  the bureaucratic requirements; and so, no new accounts are ever
  created.
  -- Stephan Zielinski, "KNOW YOUR UNIX SYSTEM ADMINISTRATOR"

Re: finding symlinks without target

[Paul Lew]

In message <19980123154701.05885@math.fu-berlin.de>, Sven Guckes writes:
 >Hi!
 >
 >Problem:
 > Find (and print) all symbolic links without a target within the
 > current dirtree.

The old zsh (dont remember version) will show bad symbolic links with
an '&' appended instead of '@' when showing partial completed
filenames.  What happen to that code?  I found I miss that feature.
Will come handy in this case.

Re: finding symlinks without target

[Bruce Stephens]

schaefer@brasslantern.com said:
> However, this appears to do the trick:
> 	echo **/*(@-^./=%p)
> All symlinks that don't point to files, directories, sockets, devices,
> or named pipes.  Whew. 

It's zany, sure.  I'm tempted to suggest a special non-existent file 
qualifier, which would expand to files that don't exist, which you could then 
use in this context, but that's probably a bit expensive if you use it in any 
other context.  And a special combination qualifier of ./=%p is probably not 
useful enough to add either.  So Bart's solution is probably as simple as it's 
going to get.

Re: finding symlinks without target

[Bart Schaefer]

On Jan 23,  4:42pm, Bruce Stephens wrote:
} Subject: Re: finding symlinks without target
}
} schaefer@brasslantern.com said:
} > (Why isn't there a glob qualifier to chase links?  **/*(@^.,@^/) would
} > appear to be perfect, but doesn't work.) 
} 
} There is, isn't there.  The - seems to be right, almost.

Indeed.  I missed that one when scanning the zsh info (probably because
I was looking for a description that used the word "chase" as in the
CHASE_LINKS option).

} How about 
} **/*(@-^.,@-^/)
} 
} Meaning those symbolic links whose referents aren't files or directories?

I should have realized before that this won't work, because that's an
-inclusive- "or" and what's wanted is an -exclusive- "or".  However,
this appears to do the trick:

	echo **/*(@-^./=%p)

All symlinks that don't point to files, directories, sockets, devices,
or named pipes.  Whew.

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Re: finding symlinks without target

[Niall Smart]

On Jan 23,  3:47pm, Sven Guckes wrote:
} Subject: finding symlinks without target
> Hi!
> 
> Problem:
> Find (and print) all symbolic links without a target within the current dirtree.
> 
> Anyone hints?

This is an abuse of your shell, there are already many C variants of
this, though I can't remember any of their names.  If you were really
desperate, you could hack something up with zsh and find.  Eg.
find . -type l -exec myscript.zsh {} \; etc etc.

Niall