The Gulpfile I created for the blogpost http://jegtnes.co.uk/blog/using-gulp-with-uncss-in-ghost-for-tiny-assets/, detailing how to use UnCSS and Gulp for Ghost.

Gulpfile.js

var gulp = require('gulp');

var sass = require('gulp-sass'); // skip this if you're working with vanilla CSS
var rename = require('gulp-rename');
var cmq = require('gulp-combine-media-queries');
var uncss = require('gulp-uncss');
var download = require('download');
var cssmin = require('gulp-cssmin');
var clean = require('gulp-clean');
var xml2js = require('gulp-xml2js');

// Upon runnning styles-build, this will be populated with all blog posts too
// See tasks find-site-files, create-sitemap, and download-rss-feed
var filesToUncss = [
              'http://jegtnes.co.uk',
              'http://jegtnes.co.uk/styleguide',
              'http://jegtnes.co.uk/portfolio',
              'http://jegtnes.co.uk/contact'
            ];

gulp.task('styles-build', ['find-site-files'], function() {
  return gulp.src('scss/style.scss') //you probably want to change this
    .pipe(sass()) // skip this if you're working with vanilla CSS
    .pipe(rename({suffix: '.min'}))
    .pipe(cmq())
    .pipe(uncss({
        html: filesToUncss
    }))
    .pipe(cssmin())
    .pipe(gulp.dest('assets/css'));
})

gulp.task('download-rss-feed', function(callback) {
  dl = download({
    url: 'http://jegtnes.co.uk/rss',
    name: 'rss.xml'
  }, './')

  dl.once('close', function() {
    callback();
  });
});

gulp.task('create-sitemap', ['download-rss-feed'], function() {
    return gulp.src('./rss.xml')
    .pipe(xml2js())
    .pipe(rename('rss.json'))
    .pipe(gulp.dest('./'));
});

gulp.task('find-site-files', ['create-sitemap'], function() {
  var json = require('./rss.json');
  json.rss.channel[0].item.forEach(function(value) {
    link = value.link[0]
    filesToUncss.push(link);
  })

  return gulp.src(['rss.json', 'rss.xml'], {read: false})
    .pipe(clean());
});

// The default task (called when you run `gulp` from cli)
gulp.task('default', ['styles-build']);