bare bones routing function for PHP.

web_app.php

<?php
// minimal routing
function web_app($routes, $req_verb, $req_path) {

  $req_verb = strtoupper($req_verb);
  $req_path = trim(parse_url($req_path, PHP_URL_PATH), '/');

  $found = false;

  if (isset($routes[$req_verb])) {

    foreach ($routes[$req_verb] as $path => $action) {

      $path = '@^'.trim($path, '/').'$@';

      if (!preg_match($path, $req_path, $capture))
        continue;

      $found = true;

      call_user_func_array($action, array_slice($capture, 1));
    }
  }

  if (!$found)
    throw new Exception('Resource not found');
}

// sample calls

// sample resource
class MyObject {
  public function methodName() {
    echo "d!";
  }
}

// sample function
function b_function() {
  echo "b!";
}

// sample routes
$routes1 = ['GET' => [
  '/a' => function () { echo "a!"; },
  '/b' => 'b_function'
]];

// more routes
$routes2 = [
  'GET' => [
    '/c/([0-9]+)' => function ($id) { echo "{$id}!"; },
    '/d' => array(new MyObject, 'methodName')
  ],
  'POST' => [
    '/e' => function () { echo "e!"; },
    '/f' => function () { echo "f!"; }
  ]
];

// serve routes
try {

  web_app(
    array_merge_recursive($routes1, $routes2),
    $_SERVER['REQUEST_METHOD'],
    $_SERVER['REQUEST_URI']
  );

} catch (Exception $e) {
  header('HTTP/1.1 404 Page not found', true);
  exit;
}
?>