- var_dump: documentation ( source)
- preg_match: documentation ( source)
- parse_url: documentation ( source)
<?php
$host = parse_url('http://www.google.co.uk/test.html');
preg_match('/(.*?)((\.co)?.[a-z]{2,4})$/i', $host['host'], $m);
$ext = isset($m[2]) ? $m[2]: '';
var_dump($ext);