运行

$brew doctor 

可查看失败原因。

homebrew-core 和homebrew-cash失败，则试着运行

$git -C "/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core" fetch --unshallow

$git -C "/usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask" fetch --unshallow

如果上面不行，请尝试：

$cd /usr/local/Homebrew/Library/Taps/homebrew/

$rm -rf homebrew-core

$git clone https://github.com/Homebrew/homebrew-core.git

如果更新homebrew-core还是失败，请尝试

$brew update-reset

如果报错443之类，请替换git源。友情链接

//www.greatytc.com/p/b26c7bc14440

https://www.cnblogs.com/sanmubai/p/13160791.html

安装homebrew，请参考
https://cloud.tencent.com/developer/article/1759415

如果还是有问题，可与我联系。