Jekyll plugin for parsing of custom variables in permalinks

_config.yml

# will substitute :author with the variable author in your file (also works with defaults). 
permalink:      /:author/:slug/
# You need to have this extra permalink_custom_vars array to tell the plugin which substitutions to make
permalink_custom_vars: ['author'] 
# Note that you don't have to include the supported variables in this list as jekyll takes care of that 
# For a complete list of variables jekyll supports, see: https://jekyllrb.com/docs/permalinks/#template-variables

permalink-custom-vars.rb

# Based on http://stackoverflow.com/a/17206081/1412255
module Jekyll
    class PermalinkRewriter < Generator
        safe true
        priority :low

        def generate(site)
            if site.config['permalink'].include? ":" # ignore presets
                site.posts.docs.each do |item|
                    item.data['permalink'] = site.config['permalink'].dup
                    site.config['permalink_custom_vars'].each do |var|
                       # if data isn't available, replace with empty
                      substitution = item.data[var].to_s or ''
                      item.data['permalink'].gsub! ":" + var, substitution 
                    end
                end
            end
        end
    end
end

To use, please put the .rb file in a directory named _plugins. See the article for more details.
Disclaimer: I only know as much ruby as I've learnt in the past 20 minutes. Safety not guaranteed.

Hello @peey
Does this work with the modern version of Jekyll? I'm trying to make it something for the pages, where if they contains a :slug, this is going to be forming the pemalink later without success.

In fact, even a simple, hardcoded replacement is ignored.

 	if p.data['slug'].include?("/test/") 
            puts("rewriting the permalink")
            permalink = p.data['permalink'] = "/newurl"
       end

Do you have any idea?
Thanks