update_rubygems_cert.rb

require "open-uri"

RUBYGEMS_VERSIONS = {
  "1.8" => {
    "url" => "https://github.com/rubygems/rubygems/releases/download/v1.8.30/rubygems-update-1.8.30.gem",
    "filename" => "rubygems-update-1.8.30.gem"
  },
  "2.0" => {
    "url" => "https://github.com/rubygems/rubygems/releases/download/v2.0.15/rubygems-update-2.0.15.gem",
    "filename" => "rubygems-update-2.0.15.gem"
  },
  "2.2" => {
    "url" => "https://github.com/rubygems/rubygems/releases/download/v2.2.3/rubygems-update-2.2.3.gem",
    "filename" => "rubygems-update-2.2.3.gem"
  }
}

current_rubygems_version = `gem --version`

puts "You currently have Rubygems #{current_rubygems_version} installed."

version  = current_rubygems_version[0..2]
url      = RUBYGEMS_VERSIONS[version]["url"]
filename = RUBYGEMS_VERSIONS[version]["filename"]

puts "Downloading Rubygems update (#{filename})..."
open(filename, 'wb') { |file| file << open(url).read }

puts "Installing #{filename}..."
`gem install --local #{filename}`

puts "Updating Rubygems..."
`update_rubygems --no-ri --no-rdoc`

puts "Cleaning up..."
`gem uninstall rubygems-update -x`

puts "Done!"