Many here are reluctant to follow off-site links. Worse, such off-site postings are apt to be ephemeral... and don't make it into the Monastery db for future reference. Please see Markup in the Monastery, Perl Monks Approved HTML tags and What shortcuts can I use for linking to other information?.

Having overcome my own reluctance, here's the pastebin content as you have it formatted:

bash-3.1$ weather --weather Newcastle | ./regex.pl
panic: top_env

======================================================================
+=======
The output from (weather --weather Newcastle) the regex would be proce
+ssing:
======================================================================
+=======

bash-3.1$ weather --weather Newcastle
   Newcastle Light Rain Late Light Rain Late. Morning Clouds. Warm.

======================================================================
+=======
                ( regex.pl )
======================================================================
+=======

#!/usr/bin/perl -w
use strict;
my $regex = qr/\s* \w+/;
while(<>)
{
        use re 'eval';
        /(?(?{$_ =~ |$regex (\w+ \w+)(?=\1)|})(?{s|$1||})|(?{s|$1 \w+|
+|}))/;
}

======================================================================
+=========
                Conclusion
======================================================================
+=========

From what i can gather from lurking google, code sub-patterns are very
+ experimental
and bug prone, ofcourse i could be wrong, seeing as i've only recently
+ adopted
Perl in the last month once finishing my final year at school.

From lurking google once more, i'm also gathering that the error messa
+ge i'm 
receiving is a bug within perl itself, and should be reported.

Bibliography:
http://www.perlmonks.org/index.pl/?node_id=368099
http://prlmnks.org/html/383052.html
[download]

It would be better, of course, to enclose (only) the code (by sections) in <c>...</c> tags and the narrative in <p>...</p> tags.

Update: re desemondo's exploration,changing the use re... to use re qw(eval debug); and then testing via checking ( perl -c 813676.pl ) produced this for me (w2k, perl 5.8.8):

Compiling REx `(?(?{$data =~ |$regex (\w+ \w+)(?=\1)|})(?{s|$1||})|(?{
+s|$1 \w+||}))'
size 15 Got 124 bytes for offset annotations.
panic: top_env
[download]