LoadEnvironmentVariables.php

<?php

// Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables
public function bootstrap(Application $app)
{
    if ($app->configurationIsCached()) { // if it cached, return empty
        return;
    }

    $this->checkForSpecificEnvironmentFile($app);

    try {
        $this->createDotenv($app)->safeLoad();
    } catch (InvalidFileException $e) {
        $this->writeErrorAndDie($e);
    }
}

// check environment.
protected function checkForSpecificEnvironmentFile($app)
{
    if ($app->runningInConsole() && ($input = new ArgvInput)->hasParameterOption('--env')) {
        if ($this->setEnvironmentFilePath(
            $app, $app->environmentFile().'.'.$input->getParameterOption('--env')
        )) {
            return;
        }
    }

    $environment = Env::get('APP_ENV');

    if (! $environment) {
        return;
    }

    $this->setEnvironmentFilePath(
        $app, $app->environmentFile().'.'.$environment
    );
}