根据来路网址关键词跳转的php代码

根据来路网址关键词跳转的php代码

<?php
if(isset($_SERVER['HTTP_REFERER'])){
  $_host=urldecode ($_SERVER['HTTP_REFERER']);
  $key="关键词";
if(strpos($_host,$key))
{
  header("Location:http://a.com/");
  exit();
}
}
?>