Ack / Grep

test.js

var util = require('util');
var exec = require('child_process').exec;

// Grep (ok)
exec("grep 'grep' test.js", function(){
	console.dir(arguments);
});

// Ack (nok)
exec("ack 'ack' test.js", function(){
	console.dir(arguments);
});

Why ???