Rails app w/ 2.2.0 embedd how to use ruby 1.8 vice 1.9

I have just downloaded an app that is based on R开发者_开发知识库ail 2.2.0 which is included in the app. I have just upgraded to Ruby 1.9 and I still have Ruby 1.8 on my machine. Is there a way I can tell this app to use Ruby 1.8 vice 1.9? Would it be easier to decouple the app from Rails 2.2.0 and upgrade it to Rails 2.3.6? If changing the rails would be easier, how do I do that?

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You could use RVM (Ruby Version Manager) which is a command line tool which allows you to easily install, manage and work with multiple ruby environments from interpreters to sets of gems.

That way you can have a different set of gems (including Rails) under Ruby 1.8 and a different set of gems under Ruby 1.9.