public function output($filename, $input)
    {
        $env = array('NODE_PATH' => $this->_settings['node_path']);

        $tmpfile = tempnam(sys_get_temp_dir(), 'miniasset_css_compressor');
        $this->generateScript($tmpfile, $input);

        $cmd = $this->_settings['node'] . ' ' . $tmpfile;
        return $this->_runCmd($cmd, '', $env);
    }