Creating your first custom module in Drupal 8 or Drupal 9

Let’s start with creating a simple custom module which will output a text message. We need to create 3 files for this->

a. Info File

b. Routing File

c. Controller

Step 1: Creating the module folder

First we need to create a custom module under [Doc Root]/modules/custom folder. Let us name the folder as first_module.

Step 2: Creating the info file

Let us first create an info file first_module.info.yml which will contain all the information about your custom module.

name: First Module
description: First Custom Module
type: module
core_version_requirement: 8.x

Step 3: Creating the routing file

Routing file is one of the most important file for Drupal module as it binds the path/URL with the controller. It’s a replacement of hook_menu() which we had in Drupal 7. Let us create a routing file named first_module.routing.yml under the module folder with the below properties.

first_module.welcome:
path: '/first/page'
defaults:
_controller:'Drupal\first_module\Controller\FirstController::firstMethod'
_title: 'Welcome to our first Drupal 8 custom module.'
requirements:
_permission: 'access content'

Step 4: Creating the Controller

As you can see in our earlier step we have already mentioned a controller class named FirstController in the controller properties. So we will create a controller with the same name. First we need to create a folder named “src” under the module folder and then create another folder “Controller” under “src”. Now we will create a controller file named FirstController.php under “Controller” folder. Let us now write a simple code for this controller which will output a message.

<?php
namespace Drupal\first_module\Controller;
use Drupal\Core\Controller\ControllerBase;

class FirstController extends ControllerBase {
  public function firstMethod() {
    return array (
    '#markup' => 'Welcome to our First Drupal 8 custom Module.'
    );
  }
}

Now Login to site and enable the newly created custom module from admin->modules. Now access the path you specified in your routing file, that is /first/page. If you get the ‘Page Not Found’ error, then clear the cache by navigating to admin->configuration->performance. Verify again and it should show the output message as below.