运行 gem环境，查看 EXECUTABLE DIRECTORY 在哪里，并将其添加到您的 PATH中

run gem enviroment and look where is the EXECUTABLE DIRECTORY and add it to your PATH

就我而言:

$ gem environment
RubyGems Environment:
  - RUBYGEMS VERSION: 1.3.5
  - RUBY VERSION: 1.8.7 (2009-06-12 patchlevel 174) [i486-linux]
  - INSTALLATION DIRECTORY: /var/lib/gems/1.8
  - RUBY EXECUTABLE: /usr/bin/ruby1.8
  - EXECUTABLE DIRECTORY: /var/lib/gems/1.8/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86-linux
  - GEM PATHS:
     - /var/lib/gems/1.8
     - /home/user/.gem/ruby/1.8
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://gems.rubyforge.org/

$ export PATH=$PATH:/var/lib/gems/1.8/bin

或添加到〜/.bashrc