How do you watch multiple files, but only run task on changed file, in Grunt.js?

Question

In learning how to use grunt, I am trying to make a simple coffee-script watcher/compiler. The problem is, if I tell the watch task to watch several files, and

Answer 1

So new to Grunt 0.4 is more named tasks

Let us give you an example!

watch: {
    package1: {
        files: [
            './modules/package1/**/*.coffee'
        ],
        tasks: ['coffee:package3']
    },
    package2: {
        files: [
            './test_packages/package2/**/*.coffee'
        ],
        tasks: ['coffee:package3']
    },
    package3: {
        files: [
            './test_packages/package3/**/*.coffee'
        ],
        tasks: ['coffee:package3']
    },
}

To run all those watch tasks, simply do grunt.registerTask('default', ['myInitialBuild', 'watch']);

Where myInitialBuild is whatever initial build (all of the files) then follow it up with a watch on each package. In reality you could do this for every file but that sounds sucky.