Connecting to MongoDB in Node.js using 10gen's default driver

mongo.connection.js

// use 10gen's mongodb driver
var mongo = require('mongodb'),
    Server = mongo.Server,
    Db = mongo.Db,
    db;

// These variables can be passed in from the commmand line or defined in your environment
var mongoServer = process.env.PETAR_MONGODB_DB_HOST,
    mongoPort = process.env.PETAR_MONGODB_DB_PORT,
    mongoDb = process.env.PETAR_DB_NAME,
    mongoUser = process.env.PETAR_MONGODB_DB_USERNAME,
    mongoPass =  process.env.PETAR_MONGODB_DB_PASSWORD;

// Print out the environment variables to make sure they exist
console.log(mongoServer, mongoPort, mongoDb, mongoUser, mongoPass);

// Initialize the server connection object
var server = new Server(mongoServer, mongoPort, {});
    db = new Db(mongoDb, server);

// Open the connection
db.open(function(err, client) {
  
    // Authenticate the user
    client.authenticate(mongoUser, mongoPass, function(err, success) {
        if (err) {
            console.log('error connecting to MongoDB: ', err);
        }
        else {
            // Do Something ...
            console.log('successfully auth to open MongoDB: ', success);
        }
    });
});

How do you set process.env variables on terminal?