In laravel 5.5+ you can, maybe earlier, you can set your server have a APP_ENV environment or server variable that the process can see (apache, command line...)
this will allow you to use a suffix or file extension on your .env files for auto loading those files...
- APP_ENV=dev :: .env.dev
- APP_ENV=production :: .env.production
much easier than other solutions.
If you want to look into how this is done, it starts with
1. application bootstrappers
protected $bootstrappers = [
    \Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables::class,
    \Illuminate\Foundation\Bootstrap\LoadConfiguration::class,
    \Illuminate\Foundation\Bootstrap\HandleExceptions::class,
    \Illuminate\Foundation\Bootstrap\RegisterFacades::class,
    \Illuminate\Foundation\Bootstrap\SetRequestForConsole::class,
    \Illuminate\Foundation\Bootstrap\RegisterProviders::class,
    \Illuminate\Foundation\Bootstrap\BootProviders::class,
];
2. LoadEnvironmentVariables
first the environment is determined…
\Illuminate\Foundation\Bootstrap\LoadConfiguration::bootstrap calls
\Illuminate\Foundation\Application::detectEnvironment
If
--env={env} for CLI then it will use that for APP_ENV.
Else
\Illuminate\Foundation\EnvironmentDetector::detectWebEnvironment
is called which uses a callback…
function () use ($config) {
            return $config->get('app.env', 'production');
        }
where app.env defaults to env('APP_ENV', 'production')
3 LoadConfiguration
\Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables::bootstrap calls...
\Illuminate\Foundation\Application::afterLoadingEnvironment
which eventually gets to
\Illuminate\Foundation\Bootstrap\LoadEnvironmentVariables::checkForSpecificEnvironmentFile
which sets the environment file based on app env IF the file exists.
        $this->setEnvironmentFilePath(
            $app, $app->environmentFile().'.'.env('APP_ENV')
        );
allowing it to load the .env.{APP_ENV} instead of .env
NOTE: Testing.
when running php unit tests. the Illuminate/Foundation will try to load the .env.testing file for configurations!