I recommend using a "canned" regex to extract all http url's and then use grep to select the .mp3's. 
use strict;
use warnings;
use Regexp::Common qw /URI/;
my $string = "xxx http://perlmonks.com yyy http://foo.mp3 zzz";
$_ = $string;
my @urls = grep {/\.mp3$/}  /($RE{URI}{HTTP})/g;
local $" = "\n";
print "@urls\n";


OutPUT:
http://foo.mp3

[download]

This approach should find all valid http url's with no false matches while saving your hair.

Bill

In reply to Re: Simple regrep question by BillKSmith
in thread Simple regrep question by monkeybus

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