学步园

<?php
$s = 'ssssssssgsdfasdasdasdasdjlkjhkjhalkasdasdjsdkajshdasdaklsjdasdhkjashgdaklsh';
$t = 'ssssssssgsdfasdjlkjhkjhalkjsdkajshdaklsjdhkjashgdaklsh';
function hh($r){
   static $n=0;
   return !$n++ ? $r[0] :''; // 先判断在加  找到一个匹配执行函数
}
$s = preg_replace_callback('/asd/','hh', $s);
var_dump($s == $t); 
?>