How to add CLI commands

Author: simpleadm

1. Magento Architecture and Customization Techniques/7. Utilize the CLI.md

@@ -31,3 +31,68 @@ Production - max speed, no errors, no file generation:
 - errors logged, not displayed
 - static not created dynamically, must be deployed
 - not need for www-data to write, pub/static can be read-only
+
+### How to add CLI commands (off-topic)
+
+Magento 2 CLI is based on the Symfony Console component.
+
+To create new CLI command you need:
+- Create command class (the recommended location is {module}/Console/Command)
+This class must extends from [\Symfony\Component\Console\Command\Command](https://github.com/symfony/console/blob/master/Command/Command.php) and have 2 methods:
+
+`configure` -  to set the name, description, command line arguments etc
+
+`execute` - is the place where you write your code
+
+```php
+<?php
+namespace Vendor\Module\Console\Command;
+
+class ExampleCommand extends \Symfony\Component\Console\Command\Command
+{
+    protected function configure()
+    {
+        $options = [
+            new \Symfony\Component\Console\Input\InputOption(
+                'param',
+                null,
+                \Symfony\Component\Console\Input\InputOption::VALUE_REQUIRED,
+                'Param description'
+            ),
+        ];
+        $this->setName('example:hello')
+            ->setDescription('Hello world command')
+            ->setDefinition($options);
+        parent::configure();
+    }
+
+    protected function execute(\Symfony\Component\Console\Input\InputInterface $input, \Symfony\Component\Console\Output\OutputInterface $output)
+    {
+        $output->writeln('hello world');
+    }
+}
+```
+
+- Declare your command in [\Magento\Framework\Console\CommandListInterface](https://github.com/magento/magento2/blob/2.2-develop/lib/internal/Magento/Framework/Console/CommandListInterface.php) using dependency injection ({module}/etc/di.xml).
+See also CommandListInterface implementation: [\Magento\Framework\Console\CommandList](https://github.com/magento/magento2/blob/2.2-develop/lib/internal/Magento/Framework/Console/CommandList.php)
+
+{module}/etc/di.xml:
+```xml
+<type name="Magento\Framework\Console\CommandListInterface">
+    <arguments>
+        <argument name="commands" xsi:type="array">
+            <item name="exampleHello" xsi:type="object">Vendor\Module\Console\Command\ExampleCommand</item>
+        </argument>
+    </arguments>
+</type>
+```
+
+- Clean the cache and compiled code directories
+
+rm -rf cache/* page_cache/* di/* generation/*
+
+###### Links
+- [Magento DevDocs - How to add CLI commands](https://devdocs.magento.com/guides/v2.2/extension-dev-guide/cli-cmds/cli-howto.html)
+- [Magento DevDocs - Command naming guidelines](https://devdocs.magento.com/guides/v2.2/extension-dev-guide/cli-cmds/cli-naming-guidelines.html)
+- [Symfony Documentation - The Console Component](https://symfony.com/doc/3.4/components/console.html)
+- [Magento - sample-module-command](https://github.com/magento/magento2-samples/tree/master/sample-module-command)