laravel/bootstrap/environment.php

<?php

/*
|--------------------------------------------------------------------------
| Load Environment Variables
|--------------------------------------------------------------------------
|
| Next we will load the environment variables for the application which
| are stored in the ".env" file. These variables will be loaded into
| the $_ENV and "putenv" facilities of PHP so they stay available.
|
*/

try
{
	Dotenv::load(__DIR__.'/../');

	Dotenv::required('APP_ENV');
}
catch (RuntimeException $e)
{
	die('Application environment not configured.'.PHP_EOL);
}

/*
|--------------------------------------------------------------------------
| Detect The Application Environment
|--------------------------------------------------------------------------
|
| Laravel takes a dead simple approach to your application environments
| so you can just specify a machine name for the host that matches a
| given environment, then we will automatically detect it for you.
|
*/

$env = $app->detectEnvironment(function()
{
	return getenv('APP_ENV');
});