/me wonders why someone wouldn't just use File::PathConvert to convert relative paths to absolute, resolve symlinks, AND handle cross platform portability...

But anyway, I decided to see if I could write a symlink resolver that returns the absolute path of symlink. As the column merlyn refers to points out, symlinks can sometimes point to symlinks, so I made sure it can handle that. This is probably not the most efficient technique, but I did write it without refering to any documentation other 'mkdir' (I forgot about the permissions mask parameter...).

I'm not a heavy *nix internals program, so if someone can point out why this way may be a bad idea, I'd like to know. *nix internals is something I'd like to have a little more experience with, but so many projects... so little time.

It will also probably break on a condition where a '/' is embedded in a filename. I don't know if this is absolutely impossible or not, perhaps someone more unix-y can tell me.

Update:Add 's' modified on regex to handle newlines in file names, and add '"./" . ' to readlink() in case symlink pointed to a directory, instead of a file. Also, '/' occuring in a file name is not a concern, per tilly, tye and merlyn. 
#!/usr/local/bin/perl -w

use strict;
use Cwd;

sub symlink_resolve
{
   my $symlink = "./" . shift;
   my ($path, $file);
   my $here = getcwd ();

   while (-l $symlink) 
   {
      ($path, $file) = $symlink =~ m|(.*/)(.*)|s;
      chdir ($path) || return undef;
      $symlink = "./" . readlink ($file) || return undef;
   }

   ($file) = $symlink =~ m|(?:.*/)(.*)|;
   $path = getcwd () || return undef;

   chdir ($here) || die;

   return "$path/$file";
}

{
   #
   #  Delete it if already exists
   #
   unlink 'sym.final', 'sym.temp/sym.link1', 'sym.link2', 'sym.temp/sy
+m.link3', 'sym.link4';
   rmdir 'sym.temp';

   mkdir 'sym.temp', 0777;
   open (FH, '>sym.final') || die;
   close FH;

   #
   #  Create a symlink: ~/sym.link4 -> ~/sym.temp/sym.link3 -> ~/sym.l
+ink2 -> ~/sym.temp/sym.link1 -> ~/sym.final
   #
   symlink ('../sym.final', 'sym.temp/sym.link1') || die;
   symlink ('sym.temp/sym.link1', 'sym.link2') || die;
   symlink ('../sym.link2', 'sym.temp/sym.link3') || die;
   symlink ('sym.temp/sym.link3', 'sym.link4') || die;

   #
   #  The test...  Should tell us that sym.link4 resolves to sym.final
   #
   die unless my $file = symlink_resolve ('sym.link4');

   print "sym.link4 resolves to $file\n"; 

   #
   #  Clean up after ourselves
   #
   unlink 'sym.final', 'sym.temp/sym.link1', 'sym.link2', 'sym.temp/sy
+m.link3', 'sym.link4';
   rmdir 'sym.temp';
}

[download]


--Chris

e-mail jcwren

In reply to (jcwren) RE: (2) Simple file question under linux by jcwren
in thread Simple file question under linux by lindex

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