Prepros is a great tool to handle your generic build tasks like compiling Sass, process images, and bundle JavaScript. I like to use this small tool to simplify my development. You must know that for an advanced build task, you always need Gulp, Webpack, or any other tool, but for most of my daily job, it is more than enough.
A custom command is your own tool, which isn’t supported by Prepos, but you still want to run it.
You can use any tool that is available through CLI, but in this article, I will show you the PurgeCSS setup.