.bashrc

...
export APP_ENV=production
...

.env.php

<?php return array (
  'DB_HOST' => 'localhost',
  'DB_NAME' => 'db_name',
  'DB_USERNAME' => 'username',
  'DB_PASSWORD' => 'password',
  'APP_ENV' => 'local'
);

.env.production.php

<?php return array (
  'DB_HOST' => 'localhost',
  'DB_NAME' => 'production_db_name',
  'DB_USERNAME' => 'production_username',
  'DB_PASSWORD' => 'production_password',
  'APP_ENV' => 'production'
);

database.php

# config/database.php
	...
	'connections' => array(

		'sqlite' => array(
			'driver'   => 'sqlite',
			'database' => __DIR__.'/../database/production.sqlite',
			'prefix'   => '',
		),

		'pgsql' => array(
			'driver'   => 'pgsql',
			'host'     => $_ENV['DB_HOST'],
			'database' => $_ENV['DB_NAME'],
			'username' => $_ENV['DB_USERNAME'],
			'password' => $_ENV['DB_PASSWORD'],
			'charset'  => 'utf8',
			'prefix'   => '',
			'schema'   => 'public',
		),

	),
	...

database2.php

# is actually: config/production/database.php
	...
	'connections' => array(

		'sqlite' => array(
			'driver'   => 'sqlite',
			'database' => __DIR__.'/../database/production.sqlite',
			'prefix'   => '',
		),

		'pgsql' => array(
			'driver'   => 'pgsql',
			'host'     => $_ENV['DB_HOST'],
			'database' => $_ENV['DB_NAME'],
			'username' => $_ENV['DB_USERNAME'],
			'password' => $_ENV['DB_PASSWORD'],
			'charset'  => 'utf8',
			'prefix'   => '',
			'schema'   => 'public',
		),

	),
	...

error

ErrorException
Undefined index: DB_HOST

start.php

# bootstrap/start.php
...

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

...