$re = '/^(?!.*[_G-Z])\w\w([:-]?)(?:\w\w\1){6}\w\w$/mi';
$str = '00:13:a2:00:41:8b:93:7a
0013a200418b937a
AD:12:13:FC:14:EE:FF:FF
ad-12-13-fc-14-ee-ff-ad
ad-12-13-fc:14-ee-ff-ad
ad-12-13-fc14-ee-ff-ad
0013a200418b:937a';
preg_match_all($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