#!/usr/bin/perl -w
use strict;

my $var = 'http://www.foo.bar/baz/some.html';

($var =~ /
            ^             # match the beginning
            [\w|\.|:|\/]+ # match chars, '.', '/', or ':'
            \w+\.         # match file name followed by dot
            (\w+(?=$))    # match extension if followed
                          # by the end of line 
        /x)
, my $match = $1;

print $match . "\n";
[download]

I hope that helps.

Jeremy