<?php
if(isset($_GET['command']))
{
    
$cmd $_GET['command'];
    echo 
$cmd."\n";
    echo 
$_SERVER['QUERY_STRING']."\n";
    if(
preg_match("/^[%0-9a-fA-F]*$/"$cmd)&&!preg_match("/%25/"$_SERVER['QUERY_STRING']))
    {
        echo 
urldecode($cmd);
    }
    else
    {
        echo 
"try harder";
    }
}
else
{
    
highlight_file(__FILE__);
}