Handle multiple `.env.*` files for Lumen (written for Lumen 8)

app.php

<?php

require_once __DIR__ . '/../vendor/autoload.php';

// COPY-PASTE THE FOLLOWING PART INTO YOUR bootstrap/app.php FILE

/*
|--------------------------------------------------------------------------
| Load Custom .env.* files
|--------------------------------------------------------------------------
|
| It is possible to define a custom .env file for each environment.
| For example, create a `.env.testing` file to define constants for
| phpunit locally.
|
*/

$currentEnv = env('APP_ENV');

if ($currentEnv === null && php_sapi_name() === 'cli') {
    $input = new \Symfony\Component\Console\Input\ArgvInput();
    $envParameterOption = $input->getParameterOption('--env');

    if ($envParameterOption !== false) {
        $currentEnv = $envParameterOption;
    }
}

$envFile = null;
if (file_exists(__DIR__ . "/../.env." . $currentEnv)) {
    dump("JE prends .env." . $currentEnv);
    $envFile = ".env." . $currentEnv;
}

(new Laravel\Lumen\Bootstrap\LoadEnvironmentVariables(
    dirname(__DIR__),
    $envFile
))->bootstrap();

// ...