This snippet prints the full path to the Rails installation directory—the path is retrieved using the RubyGems API:

   1  require 'rubygems'
   2  puts Gem.cache.search('rails').first.full_gem_path
   3  # Specify version number
   4  puts Gem.cache.search('rails', '=1.0.0').first.full_gem_path

Example output:

   1  /usr/lib/ruby/gems/1.8/gems/rails-1.0.0

To find the directory where your gems are hiding, use:

   1  gem env

There’s also the gem which command:

   1  $ gem which activesupport
   2  (checking gem activesupport-2.3.2 for activesupport)
   3  /opt/ruby-enterprise-1.8.6-20090201/lib/ruby/gems/1.8/gems/activesupport-2.3.2/lib/activesupport.rb