Creates a gzipped tar archive using vanilla Ruby and no temporary files

tar-gz.rb

require 'rubygems/package'

filenames_and_contents = {
  "filename" => "content",
}

File.open("archive.tar.gz", "wb") do |file|
  Zlib::GzipWriter.wrap(file) do |gzip|
    Gem::Package::TarWriter.new(gzip) do |tar|
      filenames_and_contents.each_pair do |filename, content|
        tar.add_file_simple(filename, 0644, content.length) do |io|
          io.write(content)
        end
      end
    end
  end
end