Example Grunt File for Watching & Compiling .coffee files in a project

Gruntfile.coffee

sourceFiles = [ '*.coffee', 'models/*.coffee', 'views/*.coffee' ]
fullPathSourceFiles = sourceFiles.map (f) -> "app/coffee/" + f
fullPathSpecFiles = sourceFiles.map (f) -> "specs/coffee/" + f

module.exports = (grunt) ->
  grunt.initConfig
    pkg: grunt.file.readJSON 'package.json'
    watch:
      coffee:
        files: fullPathSourceFiles.concat(fullPathSpecFiles)
        tasks: 'coffee'
    coffee:
      glob_to_multiple:
        expand: true
        cwd: 'app/coffee'
        src: sourceFiles
        dest: 'app/js'
        ext: '.js'
      specs:
        files: grunt.file.expandMapping(fullPathSpecFiles, "", {
          rename: (destBase, destPath) ->
            destBase + destPath.replace(/\.coffee$/, ".js").replace(/coffee\//, "js/")
        })

  grunt.loadNpmTasks 'grunt-contrib-watch'
  grunt.loadNpmTasks 'grunt-contrib-coffee'

  grunt.registerTask 'default', ['coffee']
  grunt.registerTask 'w', ['watch']

package.json

{
  "name": "Test-Grunt",
  "version": "0.1.0",
  "devDependencies": {
    "grunt": "~0.4.2",
    "grunt-contrib-jshint": "~0.6.3",
    "grunt-contrib-nodeunit": "~0.2.0",
    "grunt-contrib-uglify": "~0.2.2",
    "grunt-contrib-coffee": "~0.7.0",
    "grunt-contrib-watch": "~0.5.3"
  }
}