Initialising a DB connection from 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 1

db-env-var.php

<?php 

// Initialising a DB connection from environment vars...
$dbHost = getenv('DB_HOST');
$dbName = getenv('DB_NAME');
$dbUser = getenv('DB_USER');
$dbPass = getenv('DB_PASS');

$pdo = new \PDO("mysql:host={$dbHost};dbname={$dbName}", $dbUser, $dbPass);