Is this really the script you are using? If so you don't have a $url variable declared prior to calling $mech->get($url).

Starting your scripts with:

#!/usr/bin/perl

use strict;
use warnings;

#your script here
[download]

is good practice, and would have helped you find out what is wrong with your code. If you are new to Perl it may be worth while taking a look at some of the tutorials this site has to offer.

Also, I notice this is your first post. Welcome to the monastery, please read How do I post a question effectively? and the PerlMonks FAQ if you have not already done so. Writeup Formatting Tips is also worth reading, which would have been pointed out to you when previewing your post.

Hope this helps

Martin