$re = '/^https?:\/\/regex101\.com\/?(?:r\/(?P<link>(?:[a-zA-Z]{2}\d){2})(?:\/(?P<version>\d+)?)?)?$/m';
$str = 'http://regex101.com
http://regex101.com/
http://regex101.com/r
http://regex101.com/r/
http://regex101.com/r/FakeFakeFake
http://regex101.com/r/wY0rM7
http://regex101.com/r/wY0rM7/
http://regex101.com/r/wY0rM7/1
http://regex101.com/r/wY0rM7/11
';
preg_match_all($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