Пример рабочего Gruntfile

Gruntfile.js

module.exports = function(grunt) {
// Build a multi task "files" object dynamically.

  // Project configuration.
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    concat: {
    	js:{
    		src: [
    		
				'frontend/www/js/jquery-ui.min.js',
				'frontend/www/js/jquery-autocomplete.js',
				'frontend/www/js/jQuery.Tree.js',
				'frontend/www/js/jquery.jcarousel.min.js',
				'frontend/www/js/jquery.livequery.min.js',
				'frontend/www/js/jquery.placeholder.min.js',
				'frontend/www/js/jquery.hoverscroll.js',
				'frontend/www/js/jquery.fancybox-1.3.4.js',
				'frontend/www/js/jquery.cookie.js',
				'frontend/www/js/site-ui.js',
				'frontend/www/js/matrix.js',
				'frontend/www/js/rowSlider.js',
				'frontend/www/js/fixedmenu.js',
				'frontend/www/js/ajax-buttons.js',
				'frontend/www/js/jquery.interface.js'
    		],
    		dest: 'frontend/www/js/libs.js',

    	},
        css:{
        	src: [
    		
				'frontend/www/css/reset.css',
				'frontend/www/css/style.css',
				'frontend/www/css/button.css',
				'frontend/www/css/calendar.css',
				'frontend/www/css/cusel.css',
				'frontend/www/css/jquery.fancybox-1.3.4.css',
				'frontend/www/css/jquery-autocomplete.css',
				'frontend/www/css/jQuery.Tree.css',
				'frontend/www/css/matrix.css',
				'frontend/www/css/rowSlider.css',
				'frontend/www/css/mailoverride.css',
				'frontend/www/css/fixedmenuandthumbs.css',
    		],
    		dest: 'frontend/www/css/libs.css',

        },
      },
	uglify: {
		all:{
			files:{
	  			'frontend/www/js-min/libs.min.js': ['frontend/www/js/libs.js']
				
			}
		},
		mod:{
			files: grunt.file.expandMapping(['frontend/www/js/_modules/*.js'], 'frontend/www/js-min/_modules/', {
			    rename: function(destBase, destPath) {
			    	var filename = destPath.match(/.*\/(.*)$/)[1];
			        return destBase+filename.replace('.js', '.min.js');
			    }
			})
		}
	},
	cssmin: {
		all: {
			files: {
			  'frontend/www/css-min/libs.min.css': ['frontend/www/css/libs.css']
			}
		},
		main:{
			files: {
			  'frontend/www/css-min/styles.min.css': ['frontend/www/css/styles.css']
			}
		}
	},
	watch: {
        options: {
          spawn: false,
          livereload: true,
        },
    	all: {
	        files: ['frontend/www/js/*.js', 'frontend/www/css/*.css'],
	        tasks: ['concat','uglify', 'cssmin'],
	    	options: {
	          spawn: false,
	          livereload: true,
	        },
    	},
    	css: {
	        files: ['frontend/www/css/*.css'],
	        tasks: ['concat:css', 'cssmin'],
	    	options: {
	          spawn: false,
	          livereload: true,
	        },
    	},
   		js: {
	        files: ['frontend/www/js/*.js'],
	        tasks: ['concat:js', 'uglify'],
	    	options: {
	          spawn: false,
	          livereload: true,
	        },
    	},
    }
  });

 
  // Load the plugin that provides the "uglify" task.
  grunt.loadNpmTasks('grunt-newer');
  grunt.loadNpmTasks('grunt-contrib-uglify');
  grunt.loadNpmTasks('grunt-contrib-cssmin');
  grunt.loadNpmTasks('grunt-contrib-concat');

  // grunt.loadNpmTasks('grunt-contrib-less');
  // grunt.loadNpmTasks('grunt-reload');
  grunt.loadNpmTasks('grunt-contrib-watch');

  // Default task(s).
  grunt.registerTask('default', ['watch:all']);

};