$re = '/^(((0)|([1-9]\d?)|(1\d\d)|(2[0-5]{2}))\.?){0,3}((0)|([1-9]\d?)|(1\d\d)|(2[0-5]{2}))?$/m';
$str = '255.255.255.255
192.168.0.1
0.0.0.0
192.168.0.
192.168.0
192.1
0
33.33.33.33
2.2.99
255.255.255.255.
192.168.0.270
0.0.0.a
255.255.255. 255
192.168.0..
0.0.00.0';
preg_match_all($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