Gulpfile.js

var gulp = require('gulp');
var sequence = require('gulp-sequence');
var shell = require('gulp-shell');
var postcss = require('gulp-postcss');
var autoprefixer = require('autoprefixer');
var csswring = require('csswring');
var htmlmin = require('gulp-htmlmin');

gulp.task('css', function(cb) {
  var processors = [
    autoprefixer({
      browsers: ['last 4 versions', '> 5%']
    }),
    csswring
  ];
  return gulp.src('_site/css/*.css')
    .pipe(postcss(processors))
    .pipe(gulp.dest('_site/css'));
});

gulp.task('htmlmin', function(cb) {
  return gulp.src('_site/index.html')
    .pipe(htmlmin({
      collapseWhitespace: true
    }))
    .pipe(gulp.dest('_site/'));
});

gulp.task('watch', function(cb) {
  return gulp.src('.', {
      read: false
    })
    .pipe(shell(['jekyll serve']), {
      verbose: true
    });
});

gulp.task('jekyll-build', function(cb) {
  return gulp.src('.', {
      read: false
    })
    .pipe(shell(['jekyll build']), {
      verbose: true
    });
});

gulp.task('upload', function(cb) {
  return gulp.src('.', {
      read: false
    })
    .pipe(shell(['s3_website push']), {
      verbose: true
    });
});

gulp.task('build', function(cb) {
  return sequence('jekyll-build', ['css', 'htmlmin'], cb);
});

gulp.task('deploy', function(cb) {
  return sequence('build', ['upload'], cb);
});

gulp.task('default', ['watch']);