code: public function actionCompress($configFile, $bundleFile)
      {
          $this->loadConfiguration($configFile);
          $bundles = $this->loadBundles($this->bundles);
          $targets = $this->loadTargets($this->targets, $bundles);
          foreach ($targets as $name => $target) {
              $this->stdout("Creating output bundle '{$name}':\n");
              if (!empty($target->js)) {
                  $this->buildTarget($target, 'js', $bundles);
              }
              if (!empty($target->css)) {
                  $this->buildTarget($target, 'css', $bundles);
              }
              $this->stdout("\n");
          }
  
          $targets = $this->adjustDependency($targets, $bundles);
          $this->saveTargets($targets, $bundleFile);
  
          if ($this->deleteSource) {
              $this->deletePublishedAssets($bundles);
          }
      }
docs: Combines and compresses the asset files according to the given configuration.
  During the process new asset bundle configuration file will be created.
  You should replace your original asset bundle configuration with this file in order to use compressed files.
  @param string $configFile configuration file name.
  @param string $bundleFile output asset bundles configuration file name.