Ever find yourself deep in some code, wishing that you could figure out if a gem was installed, without trying to call against it and deal with the ensuing nastyness? Here’s how:

dependency = Gem::Dependency.new "authlogic", ">2"
specs = Gem.source_index.search dependency
puts "the gem is not installed" if specs.empty?

Thanks to rubygems-sing for the simple implementation.