Convert CSS background image paths to Shopify asset paths

gulp-shopify-css-assets.js

var gulp = require('gulp');
var $    = require('gulp-load-plugins')();
var replace = require('gulp-replace');
var rename = require("gulp-rename");

/*
Gulp task to convert CSS background image paths to Shopify asset urls,
e.g. url(/images/background.jpg) -> url({{ 'background.jpg' | asset_url }})
*/

gulp.task('fixurls', function(){
  gulp.src(['css/app.css'])
    .pipe(replace(/url\(\/?images\/(.+)\)/g, 'url({{ \'$1\' | asset_url }})'))
    .pipe(rename("style.css.liquid"))
    .pipe(gulp.dest('./css'));
});