Ruby version management (rvm) command examples.

##
# Set default ruby version
rvm --default use 1.9.3
ruby -v

##
# Install a particular version of Ruby
##
rvm install ruby-1.9.2-p320

##
# To switch back to your system ruby:
##
rvm use system
ruby -v

##
# To switch at any time to the ruby you have selected as default:
##
rvm default
ruby -v

##
# To show what ruby is currently the selected default, if any, do:
## 
rvm list default

##
# If you wish to switch back to your system ruby as default, 
# remember that RVM does not "manage" the system ruby and is "hands off".
##

# This means to set the "system" ruby as default, you reset RVM's defaults as follows.
rvm reset
ruby -v