eLore has asked for the wisdom of the Perl Monks concerning the following question:

Perhaps I've been working too many hours, or not coding enough perl, but... If I want to check the contents of a directory for symbolic links, and verify that all the links actually point to existing files, does anyone see anything that I should watch out for in the following code: 
#!/opt/perl5/bin/perl

$THISDIR="links/";

opendir THISDIR, "$THISDIR" or die "AACK: $!";
@allfiles = grep !/^\./, readdir THISDIR; # get rid of .* files
closedir THISDIR;

foreach $link (@allfiles){
        $rc=readlink "$THISDIR$link";
        !$rc and print "READLINK err: $link\n";

        -f $rc or print "File $rc does not exist\n";
}

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Replies are listed 'Best First'.
Re: verifying symbolic links
by no_slogan (Deacon) on Jul 25, 2001 at 03:06 UTC
    Your code will fail on relative symbolic links, for example: 
      /home/me/links/foo -> ../bar

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    Resolving symlinks is trickier than it seems. Let the operating system do it for you instead of trying to do it yourself with readlink. 
      print "Bad link: $link -> $rc\n" if -l $link && ! -e $link;

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[select]
      UPDATE

      Somehow my books forgot to list the "-l" file test operator. Thanks for the tip. Based on your tip, here's my new code. I need to do some additional formatting, but I think it will work quite nicely.

      #!/opt/perl5/bin/perl
$THISDIR="links/";

opendir THISDIR, "$THISDIR" or die "AACK: $!";
@allfiles = grep !/^\./, readdir THISDIR;
closedir THISDIR;

foreach $link (@allfiles){
  $rc=readlink "$THISDIR$link";

  if ((-l "$THISDIR$link") && ! -e $rc){
    print "Target for link \[$link\]:\t does not exist\n";
  }elsif (-l "$THISDIR$link" && -e $rc){
    print "Target for link \[$link\]:\t $rc\n";
  }else{
    print "File \[$link\] found in links directory\n";
  }
}

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      /UPDATE
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(MeowChow) Re: verifying symbolic links
by MeowChow (Vicar) on Jul 25, 2001 at 03:40 UTC
    From the shell: 
    find . -follow -type l

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    Sprinkle in -maxdepth to taste. 
       MeowChow                                   
               s aamecha.s a..a\u$&owag.print
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[d/l]
      Thanks for the fresh viewpoint. While I think I see what you're thinking, you should be aware that most systems (ok, HP and Solaris) recommend not using -follow with -type l.

      (from the man page) This expression should not be used with the -type l expression.

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Re: verifying symbolic links
by merlyn (Sage) on Jul 25, 2001 at 17:52 UTC
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