题目

<?phphighlight_file(__FILE__);error_reporting(0);if(isset($_POST['cmd'])){$cmd=$_POST['cmd'];if(strlen($cmd)>80){die("too long!");}if(preg_match('/\s|flag|cat|tac|more|less|head|tail|nl|sort|uniq|rev|strings|od|curl|wget|sed|awk|grep|paste|base64|xxd|php|python|perl|ruby|diff|dd|cut|cp|mv|xargs|bash|sh|nc|file|find|vi|\*|\?|\x27|"/i',$cmd)){die("hacker!");}system($cmd);}else{echo'<br><br>Give me your command! (POST: cmd)';}?>Give me your command!(POST:cmd)

过于简单，随便绕即可