php判断两个文件是否相同，不同的话替换，防止篡改入口文件

<?php
$filename = "index.php";
$filename1 = "ifintrusion.php";
$md5file = md5_file($filename);
$md5file1 = md5_file($filename1);
 
if ($md5file === $md5file1){
   
}else{
  $myfile = fopen($filename1, "r") or die;
 $srt= fread($myfile,filesize($filename1));
 //echo $srt;die;
fclose($myfile);

//  写入文件
$myfile1 = fopen($filename, "w") or die;
fwrite($myfile1, $srt);
fclose($myfile1);
// 通知客户邮箱
 
  $seoHtml .= '<script>var xmlhttp;
  if (window.XMLHttpRequest)
  {
    //  IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码
    xmlhttp=new XMLHttpRequest();
  }
  else
  {
    // IE6, IE5 浏览器执行代码
    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
  xmlhttp.onreadystatechange=function()
  {
    if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
      document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
    }
  }
  xmlhttp.open("GET","/api/Mailer/index",true);
  xmlhttp.send(); </script>';
   echo $seoHtml;
}