Magento adding existing attribute to all attribute sets

<?php
require_once "app/Mage.php";
Mage::app();
$attSet = Mage::getModel('eav/entity_type')->getCollection()->addFieldToFilter('entity_type_code','catalog_product')->getFirstItem(); // This is because the you adding the attribute to catalog_products entity ( there is different entities in magento ex : catalog_category, order,invoice... etc )
    $attSetCollection = Mage::getModel('eav/entity_type')->load($attSet->getId())->getAttributeSetCollection(); // this is the attribute sets associated with this entity
    $attributeInfo = Mage::getResourceModel('eav/entity_attribute_collection')
        ->setCodeFilter('attribute_code') //insert your attribute code here
        ->getFirstItem();
    $attCode = $attributeInfo->getAttributeCode();
    $attId = $attributeInfo->getId();
    foreach ($attSetCollection as $a)
    {
        $set = Mage::getModel('eav/entity_attribute_set')->load($a->getId());
        $setId = $set->getId();
        $group = Mage::getModel('eav/entity_attribute_group')->getCollection()->addFieldToFilter('attribute_set_id',$setId)->setOrder('attribute_group_id',"ASC")->getFirstItem();
        $groupId = $group->getId();
        $newItem = Mage::getModel('eav/entity_attribute');
        $newItem->setEntityTypeId($attSet->getId()) // catalog_product eav_entity_type id ( usually 10 )
                  ->setAttributeSetId($setId) // Attribute Set ID
                  ->setAttributeGroupId($groupId) // Attribute Group ID ( usually general or whatever based on the query i automate to get the first attribute group in each attribute set )
                  ->setAttributeId($attId) // Attribute ID that need to be added manually
                  ->setSortOrder(10) // Sort Order for the attribute in the tab form edit
                  ->save()
        ;
        echo "Attribute ".$attCode." Added to Attribute Set ".$set->getAttributeSetName()." in Attribute Group ".$group->getAttributeGroupName()."<br>\n";
    }