Usage:

rvm install ree -C --enable-shared=yes
rvm install 1.8.7 -C --enable-shared=yes
rvm install 1.9.2 -C --enable-shared=yes
rvm use 1.8.7 --default

Install on OSX http://blog.therubymug.com/blog/2010/05/20/the-install-osx.html