Ah, I see now that you are loading the "other script" via require. A more common approach would be to turn the first "script" into a Perl module, by naming it with a .pm extension and then loading it, still via require or use.

As memory management in Perl is mostly automatic, you don't have to do anything special to release the WWW::Mechanize object (as its documentation does not mention anything special either). If you want to reuse the same WWW::Mechanize object over and over, just store it in a variable at script startup and then use it from there:

package DownloadUtils;
use strict;
use vars '$mech';

sub get_mech {
    WWW::Mechanize->new();
};
$mech = get_mech();

sub get_file {
    $mech->get("$url", ':content_file' => "$file");
};

1;
[download]

If you only simply want to download some URLs, LWP::Simple might be the easier approach. But it offers less convenience when it comes to cookies etc.