$re = '/(?=\d{1,2}\s*(?:h|m))(?:(\d{1,2})\s*h)?\s*(?:\s?(\d{1,2})\s*m)?/';
$str = '8h20m 10m 8h left
8 h 30 m left
8h left
8h 20m left
57m left
1m left';
preg_match_all($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