$re = '/^([01][0-9][0-9]\.|2[0-4][0-9]\.|[0-9][0-9]\.|25[0-5]\.|[0-9]\.)([01][0-9][0-9]\.|2[0-4][0-9]\.|[0-9][0-9]\.|25[0-5]\.|[0-9]\.)([01][0-9][0-9]\.|2[0-4][0-9]\.|[0-9][0-9]\.|25[0-5]\.|[0-9]\.)([01][0-9][0-9]|2[0-4][0-9]|25[0-5]|[0-9][0-9]|[0-9])$/m';
$str = '0.0.0.0
1.1.1.1
101.101.101.101
255.255.255.255
';
preg_match_all($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