router config question

<?php
$router = new \Phalcon\Mvc\Router();
$router->add("/admin/([a-zA-Z0-9_-]+)[/]?([a-zA-Z0-9_]+)?[/]?(/.*)*", array(
        'namespace' => 'App\Controllers\Admin',
        'controller' => 1,
        'action' => 2,
        'params' => 3
));
//url: https://example.com/admin/login

question: The action is number: 2, not 'index' in linux...but in windows action is 'index'. I want to if action = '', and action map 'index', like in windows, How can i do?