$re = '/(?<sign>[-+]?)\b(?<hours>2[1-3]|[01][0-9]|[1-9]):(?<minutes>[0-5][0-9])\b/';
$str = '23:55
-13:21
+13:21
1:22
5:19
1234412231
42:48
2.48
2:48
12:159
gordon
11:87
_12:12
0:0
0:15
14:55
13:00
1:12 11:17
55:1 15:55';
preg_match_all($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