原先版本  1.7.10.2

升級後版本 2.10.0

① 開啟終端，輸入brew install git：

DavidtekiMacBook-Air:~ du$ brew install git

DavidtekiMacBook-Air:~ du$ git --version
git version 1.7.10.2 (Apple Git-33)

③ 輸入which git，發現git位於/usr/bin/git目錄下

DavidtekiMacBook-Air:~ du$ which git
/usr/bin/git

原因是：brew install git後的git安裝包在 /usr/local/git 目錄下，而系統預設/usr/bin 在/usr/local/bin之前。

所以解決方法就是將/usr/local/bin放在/usr/bin之前。

DavidtekiMacBook-Air:~ du$ brew doctor
Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry and just ignore them. Thanks!

Warning: You have unlinked kegs in your Cellar
Leaving kegs unlinked can lead to build-trouble and cause brews that depend on
those kegs to fail to run properly once built. Run `brew link` on these:
  git

Warning: /usr/bin occurs before /usr/local/bin
This means that system-provided programs will be used instead of those
provided by Homebrew. The following tools exist at both paths:
  git
  git-cvsserver
  git-shell
  git-upload-pack

Consider setting your PATH so that /usr/local/bin
occurs before /usr/bin. Here is a one-liner:
  echo 'export PATH="/usr/local/bin:$PATH"' >> ~/.bash_profile

Warning: Your Xcode (4.5.2) is outdated.
Please update to Xcode 8.2.1 (or delete it).
Xcode can be updated from the App Store.
 

然後CONTRL+X退出，Y儲存，回車

DavidtekiMacBook-Air:~ du$ pico .bash_profile

export PATH="/usr/local/bin:$PATH"

DavidtekiMacBook-Air:~ du$ git --version
git version 2.10.0

DavidtekiMacBook-Air:~ du$ brew upgrade git