code: function copyFile(from, to, cb) {
  		var err
  
  		if (from !== to) {
  			fs.createReadStream(from)
  				.on('error', errorListener).pipe(
  				fs.createWriteStream(to)
  					.on('error', errorListener)
  					.on('close', doneListener))
  		} else {
  			from = null
  			doneListener()
  		}
  
  		function errorListener(e) {
  			if (!err) err = e
  		}
  
  		function doneListener() {
  			if (!err) {
  				doCopyWatcherCount++
  				wm.add(from)
  				cb(null)
  			} else cb(err)
  		}
  	}
docs: cb(err, from)