Drupal 7: download missing modules with Drush

dl_missing.php

#!/usr/bin/env drush
<?php
/**
 * Download modules which are not found on disk but exist in system table.
 * Tested on Drupal 7.
 */
$result = db_query('SELECT * FROM system ORDER BY name');

foreach ($result as $record) {
  if (!file_exists($record->filename)) {
    $path = drupal_get_filename($record->type, $record->name);
    if (empty($path)) {
      // Project not found in Drupal installation.
      // Trying to download.
      if (drush_invoke_process('@self', 'dl', array($record->name))) {
        $downloaded_projects[] = $record->name;
      }
    }
  }

}
registry_rebuild();
if (!empty($downloaded_projects)) {
  drush_log(dt('Downloaded @projects', array('@projects' => implode(', ', $downloaded_projects))), 'ok');
}