执行 brew update 报以下错误

    1. Error: Your CLT does not support macOS 11.4.
    2. It is either outdated or was modified.
    3. Please update your CLT or delete it if no updates are available.
    4. Error: An exception occurred within a child process:
    5.   SystemExit: exit

    解决方案

    1. sudo rm -rf /Library/Developer/CommandLineTools
    3. sudo xcode-select --install # 安装 xcode-select，执行

    如果不行，可以重新安装 brew

    参考：https://www.jianshu.com/p/3f1ae7bf6b02