How to Run Magento 2 Code in External File/Script?

Sometimes you need to run Magento 2 code externally, in the following cases:

• Magento 2 integration with other frameworks or platforms that are installed on the same web server,
• quick test execution of some method, for example, cron job.

For example, create a test.php file in the Magento 2 root directory and add the following code to it:

<?php

error_reporting(E_ALL);
ini_set('display_errors', 1);

use Magento\Framework\App\Bootstrap;
require __DIR__ . '/app/bootstrap.php';

$bootstrap = Bootstrap::create(BP, $_SERVER);

$obj = $bootstrap->getObjectManager();

$state = $obj->get(Magento\Framework\App\State::class);
$state->setAreaCode('adminhtml');

$object = $obj->create(\VendorName\ModuleName\Folder\Class::class);
$object->someMethod();

VendorName\ModuleName\Folder\Class - the name of the class, you want to execute;
someMethod - the name of the method you want to execute;
Attention! Make sure the __DIR__. '/app/bootstrap.php is the correct path to the Magento 2 app/bootstrap.php file.

You can run the test.php in the web-browser or from the CLI:

php test.php