public function getUsageMessage()
    {
        foreach ($this->optionDefinitions as $def) {
            $this->usageProvider->addOptionDefinition($def);
        }
        if (empty($this->scriptName)) {
            $this->scriptName = $_SERVER['PHP_SELF'];
        }
        $this->usageProvider->setScriptName($this->scriptName);
        return $this->usageProvider->getUsageMessage();
    }