Switch rvm after git checkout

RVM Git post-checkout hook

#!/bin/bash

#Filename: .git/hooks/post-checkout
#Note: make sure to chmod +x post-checkout

CURRENT=`git branch --no-color 2> /dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/\\ \1/'`

if [ $CURRENT = "upgrade" ]; then
  rvm use r19
else
  rvm use system
fi

Better yet: http://gehling.dk/2015/09/automatic-change-rvm-environment-when-switching-git-branch/