Install REE on Mountain Lion with rbenv

install.md

1. Make sure you've install X11 from here: http://xquartz.macosforge.org/landing/.
2. Set CPPFLAGS environment variable:

$ export CPPFLAGS=-I/opt/X11/include 3. Find gcc-4.2 on your system:

$ which gcc-4.2
=> /Users/pjkelly/Developer/bin/gcc-4.2

4. Install ruby in the context of your gcc-4.2 installation:

$ CC=/Users/pjkelly/Developer/bin/gcc-4.2 rbenv install ree-1.8.7-2011.12

Source