symfony-flex-recipes/symfony/framework-bundle/3.3/config/bootstrap.php

<?php

use Symfony\Component\Dotenv\Dotenv;

require dirname(__DIR__).'/vendor/autoload.php';

// Load cached env vars if the .env.local.php file exists
// Run "composer dump-env prod" to create it (requires symfony/flex >=1.2)
if (is_array($env = @include dirname(__DIR__).'/.env.local.php')) {
    $_SERVER += $env;
    $_ENV += $env;
} elseif (!class_exists(Dotenv::class)) {
    throw new RuntimeException('Please run "composer require symfony/dotenv" to load the ".env" files configuring the application.');
} else {
    $path = dirname(__DIR__).'/.env';
    $dotenv = new Dotenv();

    // load all the .env files
    if (method_exists($dotenv, 'loadEnv')) {
        $dotenv->loadEnv($path);
    } else {
        // fallback code in case your Dotenv component is not 4.2 or higher (when loadEnv() was added)

        if (file_exists($path) || !file_exists($p = "$path.dist")) {
            $dotenv->load($path);
        } else {
            $dotenv->load($p);
        }

        if (null === $env = $_SERVER['APP_ENV'] ?? $_ENV['APP_ENV'] ?? null) {
            $dotenv->populate(array('APP_ENV' => $env = 'dev'));
        }

        if ('test' !== $env && file_exists($p = "$path.local")) {
            $dotenv->load($p);
            $env = $_SERVER['APP_ENV'] ?? $_ENV['APP_ENV'] ?? $env;
        }

        if (file_exists($p = "$path.$env")) {
            $dotenv->load($p);
        }

        if (file_exists($p = "$path.$env.local")) {
            $dotenv->load($p);
        }
    }
}

$_SERVER['APP_ENV'] = $_ENV['APP_ENV'] = $_SERVER['APP_ENV'] ?? $_ENV['APP_ENV'] ?? 'dev';
$_SERVER['APP_DEBUG'] = $_SERVER['APP_DEBUG'] ?? $_ENV['APP_DEBUG'] ?? 'prod' !== $_SERVER['APP_ENV'];
$_SERVER['APP_DEBUG'] = $_ENV['APP_DEBUG'] = (int) $_SERVER['APP_DEBUG'] || filter_var($_SERVER['APP_DEBUG'], FILTER_VALIDATE_BOOLEAN) ? '1' : '0';