Bulk update products to be in/out of stock programatically

This is an example to set all (filtered) products to be in stock with quantity of 1.

$products = Mage::getModel('catalog/product')->getCollection();
// filter your product list
$products = $products->addFieldToFilter($attribute_code, $attribute_value)->load();

foreach($products as $product){
 $stockItem = Mage::getModel('cataloginventory/stock_item')->loadByProduct($product); 
 $stockItem->setData('is_in_stock', 1);
 $stockItem->setData('qty',1);
 $stockItem->save();
}