$ sudo su
# bash
# bash < <( curl http://rvm.beginrescueend.com/releases/rvm-install-head )
# nano ~/.profile
add this line:
[[ -s “/usr/local/rvm/scripts/rvm” ]] && . “/usr/local/rvm/scripts/rvm”
# exit
$ rvm install 1.9.2
$ rvm use 1.9.2
$ ruby -v
ruby 1.9.2p0 (2010-08-18 revision 29036) [x86_64-darwin10.4.0]
$ ruby install 1.8.7
$ ruby use 1.8.7
$ ruby -v
ruby 1.8.7 (2010-08-16 patchlevel 302) [i686-darwin10.4.0]