Based on Remy Sharp's most excellent Working the Command Line
brew install zsh zsh-completions
Add oh-my-zsh
curl -L https://github.com/robbyrussell/oh-my-zsh/raw/master/tools/install.sh | sh
Make zsh default shell
chsh -s /bin/zsh
Add zsh-syntax highlighting plugin
git clone git://github.com/zsh-users/zsh-syntax-highlighting.git ~/.oh-my-zsh/custom/plugins/zsh-syntax-highlighting
Create custom theme file.
cp ~/.oh-my-zsh/themes/robbyrussell.zsh-theme ~/.oh-my-zsh/themes/scottgruber.zsh-theme
Copy and paste scottgruber.zsh-template file from this gist to update.
Open ~/.zshrc and change ZSH_THEME="robbyrussell"
to ZSH_THEME="scottgruber"
update plugins to plugins=(git zsh-syntax-highlighting)
Restart iTerm 2 source ~/.zshrc