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

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