old_contents: // partial of https://github.com/google/web-starter-kit/blob/master/gulpfile.js
  
  'use strict';
  
  // Include Gulp & Tools We'll Use
  var gulp = require('gulp');
  var browserSync = require('browser-sync');
  var $ = require('gulp-load-plugins')();
  var del = require('del');
  var reload = browserSync.reload;
  
  var path = {};
  
  // if you want to generate special css,
  // just run `gulp serve --project #{$projectName}`
  // this use in 'css' task now. it will speedup compile speed
  var projectName = $.util.env.project ? $.util.env.project : '*';
  
  path.srcDir = 'app';
  path.distDir = '_dist';
  
  gulp.task('css', function () {
    return gulp.src(path.srcDir + '/css/' + projectName + '.{styl,scss}')
      .pipe($.plumber({
          errorHandler: function (err) {
              console.log(err);
              this.emit('end');
          }
      }))
      .pipe($.if('*.styl', $.stylus()))
      .pipe($.if('*.scss', $.sass({
        outputStyle: "expanded"
      })))
      .pipe($.postcss([
        require('autoprefixer')({browsers: ['last 1 version']})
      ]))
      .pipe(gulp.dest(path.distDir + '/css/'))
  });
  
  gulp.task('js', function () {
    return gulp.src(path.srcDir + '/js/*.src.js')
      .pipe($.plumber())
      .pipe($.jshint())
      .pipe($.jshint.reporter('jshint-stylish'))
      .pipe($.babel())
      .pipe($.uglify())
      .pipe($.rename(function (path) {
        path.basename = path.basename.replace('.src', '.min');
      }))
      .pipe(gulp.dest(path.distDir + '/js/'))
  });
  
  gulp.task('html', function () {
    return gulp.src(path.srcDir + '/html/*.{html,jade}')
      .pipe($.plumber({
          errorHandler: function (err) {
              console.log(err);
              this.emit('end');
          }
      }))
      .pipe($.if('*.jade', $.jade()))
      .pipe(gulp.dest(path.distDir + '/html/'))
  });
  
  gulp.task('clean', del.bind(null, [path.distDir]));
  gulp.task('clean:css', del.bind(null, [path.distDir + '/css']));
  
  // Watch Files For Changes & Reload
  gulp.task('serve', ['default'], function () {
    browserSync({
      browser: 'google-chrome',
      notify: false,
      server: path.distDir
    });
  
    // watch the folder to reload if files was change
    gulp.watch([path.srcDir + '/js/*.js'], ['js', reload]);
    gulp.watch([path.srcDir + '/css/*.{styl,scss}'], ['css', reload]);
    gulp.watch([path.srcDir + '/html/*.{html,jade}'], ['html', reload]);
  });
  
  gulp.task('default', ['clean'], function () {
    gulp.start(['html', 'css', 'js']);
  });
  
new_contents: // partial of https://github.com/google/web-starter-kit/blob/master/gulpfile.js
  
  'use strict';
  
  // Include Gulp & Tools We'll Use
  var gulp = require('gulp');
  var browserSync = require('browser-sync');
  var $ = require('gulp-load-plugins')();
  var del = require('del');
  var reload = browserSync.reload;
  
  var path = {};
  
  // if you want to generate special css,
  // just run `gulp serve --project #{$projectName}`
  // this use in 'css' task now. it will speedup compile speed
  var projectName = $.util.env.project ? $.util.env.project : '*';
  
  path.srcDir = 'app';
  path.distDir = '_dist';
  
  gulp.task('css', function () {
    return gulp.src(path.srcDir + '/css/' + projectName + '.{styl,scss}')
      .pipe($.plumber({
          errorHandler: function (err) {
              console.log(err);
              this.emit('end');
          }
      }))
      .pipe($.if('*.styl', $.stylus()))
      .pipe($.if('*.scss', $.sass({
        outputStyle: "expanded"
      })))
      .pipe($.postcss([
        require('autoprefixer')({browsers: ['last 1 version']})
      ]))
      .pipe(gulp.dest(path.distDir + '/css/'))
  });
  
  gulp.task('js', function () {
    return gulp.src(path.srcDir + '/js/*.src.js')
      .pipe($.plumber())
      .pipe($.jshint())
      .pipe($.jshint.reporter('jshint-stylish'))
      .pipe($.babel())
      .pipe($.uglify())
      .pipe($.rename(function (path) {
        path.basename = path.basename.replace('.src', '.min');
      }))
      .pipe(gulp.dest(path.distDir + '/js/'))
  });
  
  gulp.task('html', function () {
    return gulp.src(path.srcDir + '/html/*.{html,jade}')
      .pipe($.plumber({
          errorHandler: function (err) {
              console.log(err);
              this.emit('end');
          }
      }))
      .pipe($.if('*.jade', $.jade()))
      .pipe(gulp.dest(path.distDir + '/html/'))
  });
  
  gulp.task('clean', del.bind(null, [path.distDir]));
  gulp.task('clean:css', del.bind(null, [path.distDir + '/css']));
  
  // Watch Files For Changes & Reload
  gulp.task('serve', ['default'], function () {
    browserSync({
      browser: 'google-chrome',
      notify: false,
      server: ''
    });
  
    // watch the folder to reload if files was change
    gulp.watch([path.srcDir + '/js/*.js'], ['js', reload]);
    gulp.watch([path.srcDir + '/css/*.{styl,scss}'], ['css', reload]);
    gulp.watch([path.srcDir + '/html/*.{html,jade}'], ['html', reload]);
  });
  
  gulp.task('default', ['clean'], function () {
    gulp.start(['html', 'css', 'js']);
  });
  
subject: change serve folder