framework/console/controllers/HelpController.php
public function actionIndex($command = null)
    {
        if ($command !== null) {
            $result = Yii::$app->createController($command);
            if ($result === false) {
                $name = $this->ansiFormat($command, Console::FG_YELLOW);
                throw new Exception("No help for unknown command \"$name\".");
            }

            list($controller, $actionID) = $result;

            $actions = $this->getActions($controller);
            if ($actionID !== '' || count($actions) === 1 && $actions[0] === $controller->defaultAction) {
                $this->getSubCommandHelp($controller, $actionID);
            } else {
                $this->getCommandHelp($controller);
            }
        } else {
            $this->getDefaultHelp();
        }
    }
public function actionIndex($command = null)
    {
        if ($command !== null) {
            $result = Yii::$app->createController($command);
            if ($result === false) {
                $name = $this->ansiFormat($command, Console::FG_YELLOW);
                throw new Exception("No help for unknown command \"$name\".");
            }

            list($controller, $actionID) = $result;

            $actions = $this->getActions($controller);
            if ($actionID !== '' || count($actions) === 1 && $actions[0] === $controller->defaultAction) {
                $this->getSubCommandHelp($controller, $actionID);
            } else {
                $this->getCommandHelp($controller);
            }
        } else {
            $this->getDefaultHelp();
        }
    }
Displays available commands or the detailed information
about a particular command.

@param string $command The name of the command to show help about.
If not provided, all available commands will be displayed.
@return int the exit status
@throws Exception if the command for help is unknown