php正则判断ip

<?php
$pattern = '/^(?:(?:2[0-4][0-9].)|(?:25[0-5].)|(?:1[0-9][0-9].)|(?:[1-9][0-9].)|(?:[0-9].)){3}(?:(?:2[0-5][0-5])|(?:25[0-5])|(?:1[0-9][0-9])|(?:[1-9][0-9])|(?:[1-9]))$/';
//正则匹配ip地址
$ip = "254.21.1.198";
preg_match($pattern,$ip,$out);
echo '<pre>';
print_r($out);
echo '<pre>';
$ip = "254.21.1.198a";
var_dump(preg_match($pattern,$ip));