查看源代码可以发现关键词calc.php

得到代码

 <?php
error_reporting(0);
if(!isset($_GET['num'])){
    show_source(__FILE__);
}else{
    $str = $_GET['num'];
    $blacklist = ['[a-z]', '[\x7f-\xff]', '\s',"'", '"', '`', '\[', '\]','\$', '_', '\\\\','\^', ','];
    foreach ($blacklist as $blackitem) {
        if (preg_match('/' . $blackitem . '/im', $str)) {
            die("what are you want to do?");
        }
    }
    @eval('echo '.$str.';');
}
?>

过滤掉了一些东西

fuzzing一下可用的字符