Comparison between gulp and Grunt. See http://markgoodyear.com/2014/01/getting-started-with-gulp/ for a write-up.

Gruntfile.js

/*!
 * Grunt
 * $ npm install grunt-contrib-uglify grunt-autoprefixer grunt-contrib-cssmin grunt-contrib-imagemin grunt-contrib-sass grunt-contrib-watch grunt-contrib-concat grunt-contrib-clean grunt-contrib-jshint grunt-notify --save-dev
 */

module.exports = function(grunt) {

  grunt.initConfig({

    // Sass
    sass: {
      dist: {
        options: {
          style: 'expanded'
        },
        files: {
          'dist/styles/main.css': 'src/styles/main.scss'
        }
      }
    },

    // Autoprefix
    autoprefixer: {
      options: {
        browsers: [
          'last 2 version'
        ]
      },
      dist: {
        src: 'dist/styles/main.css'
      }
    },

    // CSS minify
    cssmin: {
      dist: {
        files: {
          'dist/styles/main.min.css': 'dist/styles/main.css'
        }
      }
    },

    // JShint
    jshint: {
      files: ['src/scripts/**/*.js'],
      options: {
        jshintrc: '.jshintrc'
      }
    },

    // Concat
    concat: {
      js: {
        src: ['src/scripts/**/*.js'],
        dest: 'dist/scripts/main.js'
      },
    },

    // Uglify
    uglify: {
      dist: {
        src: 'dist/scripts/main.js',
        dest: 'dist/scripts/main.min.js'
      },
    },

    // Imagemin
    imagemin: {
      dist: {
        options: {
          optimizationLevel: 3,
          progressive: true,
          interlaced: true
        },
        files: [{
          expand: true,
          cwd: 'src/images',
          src: ['**/*.{png,jpg,gif}'],
          dest: 'dist/images'
        }]
      }
    },

    // Clean
    clean: {
      build: ['dist/styles', 'dist/scripts', 'dist/images']
    },

    // Notify
    notify: {
      styles: {
        options: {
          message: 'Styles task complete',
        }
      },
      scripts: {
        options: {
          message: 'Scripts task complete',
        }
      },
      images: {
        options: {
          message: 'Images task complete',
        }
      },
    },

    // Watch
    watch: {
      styles: {
        files: 'src/styles/**/*.scss',
        tasks: ['sass', 'autoprefixer', 'cssmin', 'notify:styles'],
      },
      scripts: {
        files: 'src/scripts/**/*.js',
        tasks: ['concat', 'uglify', 'notify:scripts'],
      },
      images: {
        files: 'src/images/**/*',
        tasks: ['imagemin', 'notify:images'],
      },
      livereload: {
        options: { livereload: true },
        files: [
          'dist/styles/**/*.css',
          'dist/scripts/**/*.js',
          'dist/images/**/*'
        ]
      }
    }
  });

  // Default task
  grunt.registerTask('default', [
    'jshint',
    'clean',
    'concat',
    'uglify',
    'sass',
    'autoprefixer',
    'cssmin',
    'imagemin'
  ]);

  // Load plugins
  grunt.loadNpmTasks('grunt-contrib-uglify');
  grunt.loadNpmTasks('grunt-autoprefixer');
  grunt.loadNpmTasks('grunt-contrib-cssmin');
  grunt.loadNpmTasks('grunt-contrib-sass');
  grunt.loadNpmTasks('grunt-contrib-watch');
  grunt.loadNpmTasks('grunt-contrib-concat');
  grunt.loadNpmTasks('grunt-contrib-jshint');
  grunt.loadNpmTasks('grunt-contrib-imagemin');
  grunt.loadNpmTasks('grunt-contrib-clean');
  grunt.loadNpmTasks('grunt-notify');

};

gulpfile.js

/*!
 * gulp
 * $ npm install gulp-ruby-sass gulp-autoprefixer gulp-minify-css gulp-jshint gulp-concat gulp-uglify gulp-imagemin gulp-notify gulp-rename gulp-livereload gulp-cache del --save-dev
 */

// Load plugins
var gulp = require('gulp'),
    sass = require('gulp-ruby-sass'),
    autoprefixer = require('gulp-autoprefixer'),
    minifycss = require('gulp-minify-css'),
    jshint = require('gulp-jshint'),
    uglify = require('gulp-uglify'),
    imagemin = require('gulp-imagemin'),
    rename = require('gulp-rename'),
    concat = require('gulp-concat'),
    notify = require('gulp-notify'),
    cache = require('gulp-cache'),
    livereload = require('gulp-livereload'),
    del = require('del');

// Styles
gulp.task('styles', function() {
  return sass('src/styles/main.scss', { style: 'expanded' })
    .pipe(autoprefixer('last 2 version'))
    .pipe(gulp.dest('dist/styles'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(minifycss())
    .pipe(gulp.dest('dist/styles'))
    .pipe(notify({ message: 'Styles task complete' }));
});

// Scripts
gulp.task('scripts', function() {
  return gulp.src('src/scripts/**/*.js')
    .pipe(jshint('.jshintrc'))
    .pipe(jshint.reporter('default'))
    .pipe(concat('main.js'))
    .pipe(gulp.dest('dist/scripts'))
    .pipe(rename({ suffix: '.min' }))
    .pipe(uglify())
    .pipe(gulp.dest('dist/scripts'))
    .pipe(notify({ message: 'Scripts task complete' }));
});

// Images
gulp.task('images', function() {
  return gulp.src('src/images/**/*')
    .pipe(cache(imagemin({ optimizationLevel: 3, progressive: true, interlaced: true })))
    .pipe(gulp.dest('dist/images'))
    .pipe(notify({ message: 'Images task complete' }));
});

// Clean
gulp.task('clean', function() {
  return del(['dist/styles', 'dist/scripts', 'dist/images']);
});

// Default task
gulp.task('default', ['clean'], function() {
  gulp.start('styles', 'scripts', 'images');
});

// Watch
gulp.task('watch', function() {

  // Watch .scss files
  gulp.watch('src/styles/**/*.scss', ['styles']);

  // Watch .js files
  gulp.watch('src/scripts/**/*.js', ['scripts']);

  // Watch image files
  gulp.watch('src/images/**/*', ['images']);

  // Create LiveReload server
  livereload.listen();

  // Watch any files in dist/, reload on change
  gulp.watch(['dist/**']).on('change', livereload.changed);

});