fwtrash/inc/router.inc.php

<?php
declare(strict_types=1);

$_page = isset($_GET['p']) ? $_GET['p'] : '';

$routes = [
  'doppelklinge' => 'doppelklinge',
  'vermessung' => 'vermessung',
  'knochen' => 'knochen',
  'default' => 'default'
];

ob_start();

require_once __DIR__ . "/../pages/{$routes[array_key_exists($_page, $routes)?$_page:'default']}.php";

$_content = ob_get_contents();
ob_end_clean();