settings.local.php

<?php

/**
 * @file
 * Local development override configuration feature.
 *
 * To activate this feature, copy and rename it such that its path plus
 * filename is 'sites/default/settings.local.php'. Then, go to the bottom of
 * 'sites/default/settings.php' and uncomment the commented lines that mention
 * 'settings.local.php'.
 *
 * If you are using a site name in the path, such as 'sites/example.com', copy
 * this file to 'sites/example.com/settings.local.php', and uncomment the lines
 * at the bottom of 'sites/example.com/settings.php'.
 */

/**
 * Load environment specific override configuration, if available.
 *
 * Keep this code block at the beginning of this file to take full effect.
 */

$dotenv = new Dotenv\Dotenv(dirname($app_root));

$dotenv->load();
$dotenv->required('MYSQL_DATABASE')->notEmpty();
$dotenv->required('MYSQL_HOSTNAME')->notEmpty();
$dotenv->required('MYSQL_PASSWORD');
$dotenv->required('MYSQL_PORT')->notEmpty();
$dotenv->required('MYSQL_USER')->notEmpty();

/**
 * Database settings.
 */
$databases['default']['default'] = [
  'database' =>  getenv('MYSQL_DATABASE'),
  'driver' => 'mysql',
  'host' => getenv('MYSQL_HOSTNAME'),
  'namespace' => 'Drupal\\Core\\Database\\Driver\\mysql',
  'password' => getenv('MYSQL_PASSWORD'),
  'port' => getenv('MYSQL_PORT'),
  'prefix' => '',
  'username' => getenv('MYSQL_USER'),
];

/**
 * Include environment specific override configuration file, if available.
 *
 * Use settings.env.<ENV>.php to override variables on secondary (staging,
 * development, etc) installations of this site. Typically used to disable
 * caching, JavaScript/CSS compression, re-routing of outgoing emails, and
 * other things that should not happen on development and testing sites.
 */
$environment = getenv('DRUPAL_ENV');

if ($environment && file_exists($app_root . '/' . $site_path . '/settings.env.' . $environment . '.php')) {
  require_once $app_root . '/' . $site_path . '/settings.env.' . $environment . '.php';
}

/**
 * Override site mail.
 */
if (getenv('DRUPAL_SITE_MAIL')) {
  $config['system.site']['mail'] = getenv('DRUPAL_SITE_MAIL');
}

/**
 * Override temporary path.
 */
if (getenv('DRUPAL_PATH_TEMP')) {
  $config['system.file']['path']['temporary'] = getenv('DRUPAL_PATH_TEMP');
}

/**
 * Stage file proxy.
 */
if (getenv('DRUPAL_STAGE_FILE_PROXY_ORIGIN')) {
  $config['stage_file_proxy.settings']['origin'] = getenv('DRUPAL_STAGE_FILE_PROXY_ORIGIN');
}