たとえば

#!/usr/bin/perl

use strict;
use warnings;
use LWP::UserAgent;
use HTTP::Request::Common;

my $req = POST(
    "http://example.com/",
    Content => { key1 => 'val1', key2 => 'val2' },
   );				# HTTP::Request
$req->header( Host => $req->uri->host_port );
$req->uri->host("localhost:8888");
print "-- request --\n";
print $req->as_string;

my $ua = LWP::UserAgent->new;
my $res = $ua->request($req);
print "-- response --\n";
print $res->content;