Here's some code I pulled out of perldoc lwpcook and modified to use the POST request to grab this very question:

use HTTP::Request::Common qw( POST );

use LWP::UserAgent;

my $ua = new LWP::UserAgent;

my $req = POST 'http://perlmonks.org/index.pl', [node_id => '20494'];
print $ua->request($req)->as_string;
[download]

HTTP::Request::Common handles quoting and encoding for you. If you like your way better, you'll need the following:

 $req->content_type('application/x-www-form-urlencoded');
$req->content('node_id=20494');
[download]

before you call $ua->request() on it.