CodeIgniter: redirect everything except controllers

// put this in application/config/routes.php

$route['default_controller'] = "welcome";
$route['scaffolding_trigger'] = "";
$controllers = glob(APPPATH."controllers/*.php");
$route_string = "";
foreach($controllers as $controller) {
    $controller = str_replace("../system/application/controllers/", "", $controller);
    $controller = str_replace(".php", "", $controller);
    
    if($route_string == "") $route_string .= $controller;
    else $route_string .= "|".$controller;
}
$route['^(?!'.$route_string.')\S*'] = "go"; // if not a controller, is sent to "go" controller

// more routes below