brew install ruby-build

install.sh

brew install ruby-build
==> Installing ruby-build dependency: rbenv
==> Downloading https://github.com/sstephenson/rbenv/tarball/v0.3.0
######################################################################## 100.0%
Warning: The cleaning step did not complete successfully
Still, the installation was successful, so we will link it into your prefix
==> Caveats
To enable shims and autocompletion add to your profile:
  if which rbenv > /dev/null; then eval "$(rbenv init -)"; fi

To use Homebrew's directories rather than ~/.rbenv add to your profile:
  export RBENV_ROOT=/usr/local/opt/rbenv
==> Summary
/usr/local/Cellar/rbenv/0.3.0: 32 files, 168K, built in 2 seconds
==> Installing ruby-build
==> Downloading https://github.com/sstephenson/ruby-build/tarball/v20121204
######################################################################## 100.0%
==> ./install.sh
/usr/local/Cellar/ruby-build/20121204: 60 files, 264K, built in 2 seconds