require 'facebook.php';

$facebook = new Facebook(array(
  'appId'  => 'YOUR_APP_ID',
  'secret' => 'YOUR_APP_SECRET',
));

//Get User ID

$user = $facebook->getUser();

if ($user) {
  try {
    
    echo $user;
    
  } 
  catch (FacebookApiException $e) 
  {
    $user = null;
  }
} else {
  die('<script>top.location.href="'.$facebook->getLoginUrl().'";</script>');
}