Make RubyGems think that a gem is already installed.
gem fake GEMNAME gem fake --version VERSION GEMNAME
The default version is 99.0.0, which ought to be higher than any genuine gem.
There are two use cases for this gem.
The first is when the system package manager provides some libraries natively. For example, Ubuntu supplies a pre-built nokogiri library. Instead of fetching all the prerequisites and compiling, you can just do:
sudo apt-get install libnokogiri-ruby
But if you subsequently install a gem that requires on Nokogiri, you'll have to build Nokogiri via RubyGems, because RubyGems doesn't know that it's already available. Now, you can make RubyGems think that it's already installed:
sudo gem fake --version 1.3.1 nokogiri
Anything that's happy with version 1.3.1 of Nokogiri will install without further effort. (If you need a newer version, of course, you're stuck with the hard way.)
Does anyone want to install Hoe, RubyForge, etc., just because some gem erroneously specified it as a requirement?
gem fake hoe rubyforge
They won't come back 'round here no more.