Using environment variables. From the article: The 12 Factor PHP App - Part 1, http://www.modernphpbook.com/articles/the-12-factor-php-app-part-1 - Fig 3

env-vars.php

<?php 

// get the environment variable and parse it:
$url = parse_url(getenv('DATABASE_URL'));

// construct the data source name:
$scheme = $url['scheme'];
$host   = $url['host'] . ':' . $url['port'];
$dbname = trim($url['path'], '/'); // '/application_db' -> 'application_db'
$dsn = "{$scheme}:host={$host};dbname={$path}";

// connect to the database:
$pdo = new \PDO($dsn, $url['user'], $url['pass']);