brew安装fatal: not in a git directory

Solution:
Execute brew -v to view the prompt. The homebrew-core and homebrew-cask directories are not considered safe directories by git, and two lines of commands are required to add them.

lixu@lixudeMacBook-Pro ~ % brew -v
Homebrew 3.4.1
fatal: unsafe repository ('/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core' is owned by someone else)
To add an exception for this directory, call:

	git config --global --add safe.directory /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core
Homebrew/homebrew-core (no Git repository)
fatal: unsafe repository ('/usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask' is owned by someone else)
To add an exception for this directory, call:

	git config --global --add safe.directory /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask
Homebrew/homebrew-cask (no Git repository)

Execute the following command according to the prompt

git config --global --add safe.directory /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core
git config --global --add safe.directory /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask

Finish