$re = '/^(([0-9A-Fa-f]{2}[:-]?){5}[0-9A-Fa-f]{2})-(([0-9A-Fa-f]{2}:?){4})$/';
$str = 'aa:aa:aa:aa:aa:aa-55:56:57:58:';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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