gistfile1.rb

require 'yaml'

def dir_to_array(dir)
  Dir.entries(dir).reject { |e| ['.', '..'].include? e }.map { |entry|
    if File.directory? "#{dir}/#{entry}"
      { "#{entry}" => dir_to_array "#{dir}/#{entry}"}
    else
      entry
    end
  }
end

File.open('books.yml', 'wb') do |out|
    YAML.dump({"books" => dir_to_array(ARGV[0])}, out)
end