Drupal 8 custom module

Using below easy steps you can able to create custom module in Drupal 8.

// Steps.
1. Go to your root directory
2. Navigate to modules folder
3. Under modules folder, create two directories (Contrib, Custom)
4. Under custom folder, create your first module folder (first_module)

// Create first_module.info.yml in the root of the first_module directory.

     
name: First Module
description: An experimental module to build our first Drupal 8 module
package: Custom
type: module
version: 1.0
core: 8.x

// .module file not mandatory in Drupal 8 for custom module.
#. Create src & Controller folder under first_module.
#. Within the Controller folder, create a file called FirstController.php.
// Write below codes under FirstController.php

     
namespace Drupal\first_module\Controller; 
use Drupal\Core\Controller\ControllerBase; 
class FirstController extends ControllerBase {
  public function content() {
  return array(
      '#type' => 'markup',
      '#markup' => t('Hello world'),
    );
  }
}

// Add a route file.
#. Create a file called first_module.routing.yml
#. Add the following code to first_module.routing.yml

     
first_module.content:
  path: '/first'
  defaults:
    _controller: 'Drupal\first_module\Controller\FirstController::content'
    _title: 'Hello world'
  requirements:
    _permission: 'access content'

// View the content.
If you now go to /first, you will see the Hello World message that is being returned from the controller.

// Create menu link.
#. In your module root, create first_module.links.menu.yml
# . Add the following:

     
first_module.admin:
  title: 'First module settings'
  description: 'A basic module to return hello world'
  parent: system.admin_config_development
  route_name: first_module.content
  weight: 100

#. Clear the cache and then you should see the menu item under configuration -> development.
#. Click on the menu item and it will take you to /first.

A custom block.

// First, we need to create a new plugin for the module.
// [Plugins] are new in Drupal 8 and provide swappable pieces of functionality.

#. To get started, create a new directory in the module’s src folder called Plugin.
This is where you can store all of your plugins for this module.

#. Then create a folder called Block. A block is a plugin type.
#. And inside the Block folder, create a file called HelloBlock.php.

#. Another new concept to Drupal that we need to use for the block is Annotations.
 In order for Drupal to find your block code, you need to implement a code comment in a specific way, called an Annotation.

// The full code for HelloBlock.php

     
 $this->t('Hello, World!'),
    );
  }
 
}

See this link for how to enable & display the module.

Reference link:
-- Create your first Drupal 8 module

Refer below image for folder structure. 

You can download full code of this module from here : https://github.com/kali-dasan/D8-custom_module

Drush custom command - Drush in our custom module

Drush is a very powerful command line tool to manage Drupal site.

Other than core Drush command, we can also write our own custom drush command to perform some task like cron setup, etc, ...

we can do it by using below 3 steps.

Steps :
1) Write hook_drush_help.
2) Write hook_drush_command.
3) Write drush_hook_command.

1) hook_drush_help.

/**
 * Implements hook_drush_help().
 */
function my_module_drush_help($command) {
  switch ($command) {
    case 'drush:test-import':
     return dt('Import test contents.');
  }
}

2) hook_drush_command.

/**
 * Implements hook_drush_command().
 */
function my_module_drush_command() {
  $items = array();
  $items['test-import'] = array(
    'description' => dt('Import test contents.'),
    'arguments'   => array(
      'arg1'    => dt('An optional example argument'),
    ),
    'examples' => array(
      'Standard example' => 'drush test-import',
      'Argument example' => 'drush test-import 5',
    ),
    'aliases' => array('ti'),
  );
  return $items;
}

3) drush_hook_command.

/**
 * Implements drush_hook_command().
 */
function drush_my_module_test_import($arg = NULL) {
  // print arg if any.
  if (isset($arg)) {
   drush_print($arg);
  } 
  drush_log('importing test contents...', 'ok');
}

Now Goto drush command line interface and try > drush test-import or > drush ti