Install the latest Homebrew precompiled Ruby with the chruby Ruby version switcher.

brew-ruby-chruby.sh

# Install Homebrew if you haven't already:
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

# Install the latest stable Ruby and chruby:
brew install ruby chruby

# Symlink brew Ruby to ~/.rubies where chruby will autodetect it:
mkdir -p "$HOME/.rubies"
ln -s "$(brew --prefix ruby)" "$HOME/.rubies/ruby-$(brew ls --versions ruby | cut -d" " -f2)"

# Add the following to your ~/.bashrc or ~/.zshrc file
# and run them once in your terminal or reload your terminal:
source /usr/local/opt/chruby/share/chruby/chruby.sh
source /usr/local/opt/chruby/share/chruby/auto.sh

# Switch to brew Ruby:
chruby ruby

# Switch to system Ruby:
chruby system

# Optionally set a default Ruby:
echo "ruby-2" > "$HOME/.ruby-version"