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// D7
variable_set('my_data', 'foo');
$data = variable_get('my_data', 'bar');
variable_del('my_data');

// D8
\Drupal::state()->set('my_data', 'foo');
$data = \Drupal::state()->get('my_data') ?: 'bar';
\Drupal::state()->delete('my_data');

// See https://www.drupal.org/node/1787318

Configuration management

/**
 * EXPORT
 */ 

$ drupal config:export [options]
$ ce

/**
 * IMPORT
 */ 

$ drupal config:import [options]
$ ci

/**
 * Override config value in active configuration.
 */

$ drupal config:override [arguments]
$ co

Ex: $ drupal config:override contact.settings flood.limit 10



/**
 * Drupal settings.php configuration
 * see https://www.drupal.org/docs/8/configuration-management/changing-the-storage-location-of-the-sync-directory
 */


$config_directories[CONFIG_SYNC_DIRECTORY] = 'sites/default/sync';