Read node.js by line from endless stream

I have an endless command line stream - namely logs from my heroku app - and want to parse it by line into node.js.

I have tried various approaches, like with the readline interface (does nothing):

var command = 'heroku logs --app myapp --tail';

var heroku    = Npm.require('child_process').exec(command);
var readline = Npm.require('readline');

var rl = readline.createInterface({
    input: heroku.stdin,
    output: process.stdout
});

rl.on('line', function(log) {
    console.log(log);
});

Or with just raw exec, that does return an initial buffer, but does not read continously from the process:

var command = 'heroku logs --app myapp --tail';

var heroku    = Npm.require('child_process').exec(command);

heroku.stdout.setEncoding('utf8');

heroku.stdout.on('data', function (data) {
    console.log('stdout: ' + data);
});

I did not get it to work with spawn - even though I think it may be correct.

What would be a better approach (I'm using meteor, hence the added Npm).