Installing a major Ruby implementation without XCode

No don't update the Apple supplied ruby as that could affect existing ruby scripts and will get overridden in a System Upgrade.

To install ruby see the Download Ruby page from the ruby language website (the main page of which you should have bookmarked)

The two ways that you should consider are

1. Download the RVM. Then edit your .bash_profile to put the bin path of the install at the front of your PATH.

2. Use a package manager (e.g. Macports, Fink, Homebrew) and put their path at the front of your PATH ( I would use this only if you have C libraries that you need as well)

Solved by re-installing Xcode, CLI tools, openssl (brew), autoconf (brew), automake (brew) and apple-gcc42 (brew). After re-installing I ran rvm get head (thanks to @mpapis in #rvm on freenode). rvm get head gave me the following:

  * WARNING: you have 'rvm_configure_env' in /etc/rvmrc, run the following to fix:

      sudo sed -i'' -e "s#rvm_configure_env=('LDFLAGS=-L/opt/sm/pkg/active/lib CFLAGS=-I/opt/sm/pkg/active/include CPATH=/opt/sm/pkg/active/include')#rvm_configure_env=('LDFLAGS=-L/opt/sm/pkg/active/lib' 'CFLAGS=-I/opt/sm/pkg/active/include' 'CPATH=/opt/sm/pkg/active/include')#" /etc/rvmrc

  * No new notes to display.

# RVM:  Shell scripts enabling management of multiple ruby environments.
# RTFM: https://rvm.io/
# HELP: http://webchat.freenode.net/?channels=rvm (#rvm on irc.freenode.net)
# Cheatsheet: http://cheat.errtheblog.com/s/rvm/
# Screencast: http://screencasts.org/episodes/how-to-use-rvm

# In case of any issues read output of 'rvm requirements' and/or 'rvm notes'

Upgrade of RVM in /usr/local/rvm/ is complete.

# hinmn,
#
#   Thank you for using RVM!
#   I sincerely hope that RVM helps to make your life easier and
#   more enjoyable!!!
#
# ~Wayne

RVM reloaded!

After that I just ran:

sudo sed -i'' -e "s#rvm_configure_env=('LDFLAGS=-L/opt/sm/pkg/active/lib CFLAGS=-I/opt/sm/pkg/active/include CPATH=/opt/sm/pkg/active/include')#rvm_configure_env=('LDFLAGS=-L/opt/sm/pkg/active/lib' 'CFLAGS=-I/opt/sm/pkg/active/include' 'CPATH=/opt/sm/pkg/active/include')#" /etc/rvmrc

And everything worked out :)