set tax class on collection

taxclass.php

error_reporting(E_ALL | E_STRICT);
define('MAGENTO_ROOT', getcwd());
$mageFilename = MAGENTO_ROOT . '/app/Mage.php';
require_once $mageFilename;
Mage::setIsDeveloperMode(true);
ini_set('display_errors', 1);
umask(0); 
Mage::app();

$productIds = Mage::getResourceModel('catalog/product_collection')->getAllIds();

Mage::getSingleton('catalog/product_action')->updateAttributes(
    $productIds, 
    array('tax_class_id' => 2),
    0
);