Allow requiring of global gems from outside of the Gemfile

unbundled_require.rb

# Include this in your .irbrc
def unbundled_require(gem)
  if defined?(::Bundler)
    spec_path = Dir.glob("#{Gem.dir}/specifications/#{gem}-*.gemspec").last
    if spec_path.nil?
      warn "Couldn't find #{gem}"
      return
    end

    spec = Gem::Specification.load spec_path
    spec.activate
  end

  begin
    require gem
    yield if block_given?
  rescue Exception => err
    warn "Couldn't load #{gem}: #{err}"
  end
end

# Then use like this
unbundled_require 'wirb' do
  Wirb.start
end

Ah ok. I've well and truly given up on 1.8, so this will probably only work on 1.9. But let me know if you get it working!

I added a fix à la the Gemfile for requiring a gem with a different name than the gem itself: https://gist.github.com/3894925