$re = '/^([a-zA-Z]{2}\d{4})(?!-\d)(L\d|Transit|T$)?/m';
$str = 'AB1201
AB-1201
AB1201-T
AB-12-01L1
AB1201-TER
AB1201 Transit
AB1201EFH
AB1201-02
AB1201-EFH';
preg_match_all($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