Magento get current full Action controller name in Observer

observer.php

<?php
        /*
         * Get full Action controller name in Observer
         */
        $request = Mage::app()->getRequest();
        $module = $request->getControllerModule();
        $module_controller = $request->getControllerName();
        $module_controller_action = $request->getActionName();
        
        $fullActionName = $module."_".$module_controller."_".$module_controller_action;
       
        echo $fullActionName; 
        Mage::log($fullActionName, null,'custom.log');