Switch Ruby and Rails Versions

Once you've done the one-time setup of rvm, some ruby versions, and Rails:

$rails -v

Rails 3.0.1

$rails _2.3.10_ -v

Rails 2.3.10

$ruby -v

ruby 1.8.7 (2009-06-12 patchlevel 174) [universal-darwin10.0]

$rvm -use 1.9.1

$ruby -v

ruby 1.9.1p378 (2010-01-10 revision 26273) [i386-darwin10.4.0]

$rvm -use system

$ruby -v        

ruby 1.8.7 (2009-06-12 patchlevel 174) [universal-darwin10.0]

Once the Rails app is created, you manipulate the Rails version from the environment.rb.