Output content of Blocks to Log file

magento_blocks_log.php

        $output = '===============================================================' . PHP_EOL;
        //$output .= 'START:' . $ctrl->getFullActionName() . PHP_EOL;
        $output .= 'START:' . PHP_EOL;

        $blocks = Mage::app()->getLayout()->getAllBlocks();
        foreach ($blocks as $blockName => $block) {
            $output .= 'BLOCK: ' . $blockName . PHP_EOL;
            //$output .= $observer->getLayout()->getBlock($blockId )->toHTML();
            $output .= $block->toHTML();
            $output .= PHP_EOL . PHP_EOL;
        }

        Mage::log($output, Zend_Log::WARN, 'test.log');