Automatic cache busting using Git commit in Symfony2

assets_version.php

<?php
// app/config/assets_version.php

$container->loadFromExtension('framework', array(
    'templating'      => array(
        'engines' => array('twig'),
        'assets_version' => exec('git rev-parse --short HEAD'),
    ),
));

config.yml

# app/config/config.yml

imports:
    - { resource: parameters.yml }
    #...
    - { resource: assets_version.php }