brewでインストール
$ brew install git
下記ファイルを移動
$ cd /usr/local/Cellar/git/2.17.0/etc
$ mv git-prompt.sh /usr/local/git/contrib/completion/
$ mv git-completion.bash /usr/local/git/contrib/completion/
.bashrcに記述
$ sudo vim ~/.bashrc
# git settings
source /usr/local/git/contrib/completion/git-prompt.sh
source /usr/local/git/contrib/completion/git-completion.bash
GIT_PS1_SHOWDIRTYSTATE=true
export PS1='\[\033[32m\]\u@\h\[\033[00m\]:\[\033[34m\]\w\[\033[31m\]$(__git_ps1)\[\033[00m\]\$ '
.bashrcを再読み込み
$ source ~/.bashrc