php modify self content

http://trac.symfony-project.org/browser/branches/1.2/lib/autoload/sfCoreAutoload.class.php#L122

$content = preg_replace('/protected \$classes = array *\(.*?\)/s', 'protected $classes = '.var_export($classes, true), file_get_contents(__FILE__));
file_put_contents(__FILE__, $content);