#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;
use URI;

my $text = <<END;
this is some plain text
here is a link: [link://forum] and here is another: 
[mentors://pil_description|Partnerships in Learning]
END

$text =~ s!
          \[
            (\w+)
            ://
            ([\w-]+)
            (?:|([^]]+))?
          \]
          !print("'$1' '$2' '$3'\n")!gsex;

##</code><code>##

'link' 'forum' ''
'mentors' 'pil_description' '|Partnerships in Learning'
Use of uninitialized value in concatenation (.) or string at test.pl line 13.