/usr/local/lib/ruby/1.8/irb/completion.rb:10:in `require': no such file to load -- readline (LoadError) 
        from /usr/local/lib/ruby/1.8/irb/completion.rb:10 
        from /usr/local/lib/ruby/1.8/irb/init.rb:252:in `require' 
        from /usr/local/lib/ruby/1.8/irb/init.rb:252:in `load_modules' 
        from /usr/local/lib/ruby/1.8/irb/init.rb:250:in `each' 
        from /usr/local/lib/ruby/1.8/irb/init.rb:250:in `load_modules' 
        from /usr/local/lib/ruby/1.8/irb/init.rb:21:in `setup' 
        from /usr/local/lib/ruby/1.8/irb.rb:54:in `start' 
        from /usr/local/bin/irb:13 

   sudo apt-get install libncurses5-dev libreadline5-dev 進行安裝 

cd /usr/src/ruby-1.8.7/ext/readline 
ruby extconf.rb 
make 
sudo make install