How to access variables declared in main app.js in separate route files in node.js Express 2.5.5?

I just started using a new version of Express (2.5.5) that by default creates a ./routes directory along with ./views and ./public

Inside of routes there is a index.js file which contains:

/*
 * GET home page.
 */

exports.index = function(req, res){
  res.render('index', { title: 'Express' })
};

by default (after running express from the commandline) and this is the routes section in the main app.js:

// Routes

app.get('/', routes.index);

I've set up a variable for a redis client in the main app.js:

var redis = require('redis'),
    db = redis.createClient();

and I was wondering how I could access the methods of db (and whatever other modules I require in app.js) in the files contained in ./routes