php password密码验证正则表达式(8位长度限制)

<?php 
//密码验证 
$password = "zongzi_Abc_oo13a2"; 
$n = preg_match_all("/^[a-zA-Z\d_]{8,}$/",$password,$array); 
//长度是8或更多 
var_dump($array); 
?>