$ sudo apt-get install rubygems $ sudo apt-get install rubygems1.9 yoya@sakura:~$ gem 'prawn' ERROR: While executing gem ... (RuntimeError) Unknown command praw yoya@sakura:~$ gem1.9.1 'prawn' ERROR: While executing gem ... (RuntimeError) Unknown command prawn yoya@sakura:~$ gem1.8 'prawn' ERROR: While executing gem ... (RuntimeError) Unknown command prawn
$ sudo apt-get install rails $ sudo apt-get install libsinatra-ruby