Gruntfile.js

// ./Gruntfile.js
module.exports = function(grunt) {
	grunt.loadTasks('hoge');
};

Shell

$ grunt hoge
`hoge/xxx.js` is loaded!
Running "hoge" task
Hello, hoge world!

Done, without errors.

xxx.js

// ./hoge/xxx.js
module.exports = function(grunt) {
	console.log('`hoge/xxx.js` is loaded!');

	grunt.registerTask('hoge', function() {
		console.log('Hello, hoge world!');
	});
};