$re = '/^(?P<code_1>\d+-\d+)(?:\s*,\s*(?P<code_2>\d+-\d+))?(?:\s*,\s*(?P<code_3>\d+-\d+))?$/m';
$str = '21-1091, 21-1094, 21-1099';
preg_match_all($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