If you use LWP::Simple, then you don't need to use $ua->env_proxy. It does it automatically. Also, I would use LWP::Simple for simple uses such as url validation. For example, here I have a bunch of urls that I want to check for validity:

#!/usr/bin/perl

use strict;
use warnings;
use LWP::Simple;

my @pages = (
        'http://www.perlmonks.org',
        'http://www.perlmonks.com',
        'http://www.perlmonks.net',
        'http://www.perlmonks.edu',
        'http://www.perlmonks.co.uk',
        'http://perlmonks.perl.org'
);

foreach my $page(@pages) {
        if (head($page)) {
            print "Exists\n";
        }
        else {
            print "It doesn't exist\n";
       }
}
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