public function output($filename, $input)
    {
        $cmdSep = $this->_settings['version'] <= 1 ? ' - ' : '';
        $cmd = $this->_settings['node'] . ' ' . $this->_settings['uglify'] . $cmdSep . $this->_settings['options'];
        $env = array('NODE_PATH' => $this->_settings['node_path']);
        return $this->_runCmd($cmd, $input, $env);
    }