PHP DotEnv for Yii2 framework.

Then tell Composer to load the extension:

composer require yiithings/yii2-dotenv

The extension default load environment variables from .env file in your application root directory. You can change the file path and name configure in your application entry file:

define('DOTENV_PATH', '/path/to/.env');
define('DOTENV_FILE', '.env');
define('DOTENV_OVERLOAD', false);

Once the extension is installed, simply use it in your code by :

[
    'db' => [
        'username' => env('DB_USERNAME', 'root'),
        'password' => env('DB_PASS'),
    ],
]

The env function will autoload .env file, it uses the following search mechanism:

If there is a Yii class, then pass the alias @vendor or @app or @yii, Otherwise 
according to the project directory to determine.

But, if your application vendor directory is a symbol link and you no registered @vendor or @app alias before call env function, the project will not working. So you should set the @vendor alias before calling env function.