$re = '/(?<Protocol>(http(s)?)):\/\/(?<SubDomain>([a-zA-Z]{1,3}\.))?(?<Domain>[a-zA-Z0-9]{2,})\.(?<TopLevelDomain>[a-zA-Z0-9]{2,}(\.[a-zA-Z0-9]{2,})?)/m';
$str = '';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php