Example of automatically adding collections to _config.yml

build.rb

require "set"
require "pathname"
require "yaml" 

docs_folder = "resources/main-project-repo/docs/"
config = YAML.load_file "_config.yml" 

version_folders = Pathname.new(docs_folder).children.select do |c| 
    c.directory?
end

doc_versions = version_folders.collect { |pn| pn.basename.to_s }

# Add unique new collections to existing
if config["collections"]
    collections = doc_versions.concat(config["collections"])
else 
    collections = doc_versions
end

config["collections"] = Set.new(collections).to_a

print config
File.open("_config.yml", 'wb') { |f| YAML.dump(config, f) }

# Now do the actual build
jekyll build