https://ctf.bugku.com/challenges/detail/id/76.html

flag In the variable ! <?php  

error_reporting(0);
include "flag1.php";
highlight_file(__file__);
if(isset($_GET['args'])){
    $args = $_GET['args'];
    if(!preg_match("/^\w+$/",$args)){
        die("args error!");
    }
    eval("var_dump($$args);");
}
?>

http://host:port/?args=GLOBALS