$ git gui
git: 'gui' is not a git command. See 'git --help'.

Did you mean one of these?
    grep
    init
    pull
    push

[alias]
gui = !sh -c '/usr/local/git/libexec/git-core/git-gui'

alias gui='/usr/local/git/libexec/git-core/git-gui'

brew install git

$ which git
/usr/local/bin/git

$ git --version
git version 1.7.12.1

brew install git
/usr/local/opt/git/bin/git gui