Install rbenv, rbenv-build, and ruby idempotently for use in bash.Works for Ubuntu and Mac.

rbenv_ruby.sh

#!/bin/bash

if test -f $HOME/.profile
then
  PROFILE_FILE="$HOME/.profile"
elif test -f $HOME/.bash_profile
then
  PROFILE_FILE="$HOME/.bash_profile"
else
  echo "Creating a new .bash_profile file."
  touch $HOME/.bash_profile
  PROFILE_FILE="$HOME/.bash_profile"
fi

if ! test -d $HOME/.rbenv
then
  git clone git://github.com/sstephenson/rbenv.git $HOME/.rbenv
fi

if ! grep -q "export PATH=\"\$HOME/.rbenv/bin:\$PATH\"" $PROFILE_FILE
then
  echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> $PROFILE_FILE
fi

if ! grep -q "eval \"\$(rbenv init -)\"" $PROFILE_FILE
then
  echo 'eval "$(rbenv init -)"' >> $PROFILE_FILE
fi

#exec $SHELL -l
#source $PROFILE_FILE
. $PROFILE_FILE

if ! test -d $HOME/.rbenv/plugins/ruby-build
then
  git clone https://github.com/sstephenson/ruby-build.git $HOME/.rbenv/plugins/ruby-build
fi

VERSION=
until rbenv install -l | grep -q -x "  $VERSION"
do
  echo "Which version of ruby would you like to install? (example: '1.9.3-p429'): "
  read VERSION
  if ! rbenv install -l | grep -q -x "  $VERSION"
  then
    echo "Version not found! Please try again."
    sleep 1
    rbenv install -l
  fi
done

if ! rbenv versions | grep -q $VERSION
then
  rbenv install $VERSION
  rbenv rehash
else
  echo "This version is already installed!"
fi