code: public function actionUsage($action)
      {
          $result = Yii::$app->createController($action);
  
          if ($result === false || !($result[0] instanceof Controller)) {
              return;
          }
  
          /** @var Controller $controller */
          list($controller, $actionID) = $result;
          $action = $controller->createAction($actionID);
          if ($action === null) {
              return;
          }
  
          $scriptName = $this->getScriptName();
          if ($action->id === $controller->defaultAction) {
              $this->stdout($scriptName . ' ' . $this->ansiFormat($controller->getUniqueId(), Console::FG_YELLOW));
          } else {
              $this->stdout($scriptName . ' ' . $this->ansiFormat($action->getUniqueId(), Console::FG_YELLOW));
          }
  
          foreach ($controller->getActionArgsHelp($action) as $name => $arg) {
              if ($arg['required']) {
                  $this->stdout(' <' . $name . '>', Console::FG_CYAN);
              } else {
                  $this->stdout(' [' . $name . ']', Console::FG_CYAN);
              }
          }
  
          $this->stdout("\n");
      }
docs: Displays usage information for $action.
  
  @param string $action route to action
  @since 2.0.11