nodemon + express, listen port =?

I create a simple node project using express:

npm install -g express-generator
express test
cd test/ && npm install
PORT=3000 npm start

So this gets the test app up and running on port 3000. Great. Now I'd like to use nodemon to run this project. I've installed it:

npm install -g nodemon

In the gihub README it is run the same way as node. This is a bit confusing, because the new way of starting node is npm start not node. So I tried:

$ PORT=3000 nodemon ./app.js 
13 May 23:41:16 - [nodemon] v1.0.18
13 May 23:41:16 - [nodemon] to restart at any time, enter `rs`
13 May 23:41:16 - [nodemon] watching: *.*
13 May 23:41:16 - [nodemon] starting `node ./app.js`
13 May 23:41:16 - [nodemon] clean exit - waiting for changes before restart

But when I try to connect, there's nothing there. I confirmed that with:

lsof -i TCP:3000

Which returned nothing. Normally (with npm start) it returns:

COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
node    18746 user   10u  IPv4 433546      0t0  TCP *:3000 (LISTEN)

Can anyone tell whats wrong here? How is it possible to get the app to listen on the specified port with nodemon?

my setup:

npm -v
1.3.21
node -v
v0.10.24
nodemon -v
v1.0.18
express -V
4.2.0

in package.json

  "scripts":{
    // "start": "node ./bin/www"
    "start": "nodemon ./bin/www"
   }

the following would now be equivalent:

$ npm start
$ nodemon ./bin/www

This also works: Include this in your app.js (it does the same thing as the neolivz4ever said)

app.set('port', process.env.PORT || 3000);
var server = app.listen(app.get('port'), function() {
  console.log('Express server listening on port ' + server.address().port);
});

you too use define your for nodemon:

$ nodemon --inspect ./bin/www 3000