Mac HomeBrew update卡死、慢、替换源无效

关于卡死的位置可以用 brew update -v 的进度：

$ brew update -v  
 Checking if we need to fetch /usr/local/Homebrew...
 Checking if we need to fetch /usr/local/Homebrew/Library/Taps/caskroom/homebrew-cask...
 Fetching /usr/local/Homebrew...
 Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
 Checking if we need to fetch /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
 Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-cask...
 Fetching /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core...
 Fetching /usr/local/Homebrew/Library/Taps/caskroom/homebrew-cask... 

往往发生在 caskroom 与 homebrew 的 homebrew-cask 之间，具体解决办法，将这些环境变量需追加至 .zshrc

export HOMEBREW_BREW_GIT_REMOTE="https://mirrors.ustc.edu.cn/brew.git"
export HOMEBREW_CORE_GIT_REMOTE="https://mirrors.ustc.edu.cn/homebrew-core.git"
export HOMEBREW_BOTTLE_DOMAIN="https://mirrors.ustc.edu.cn/homebrew-bottles"
export HOMEBREW_API_DOMAIN="https://mirrors.ustc.edu.cn/homebrew-bottles/api"

或者，直接根据中科大指引重新安装：Homebrew USTC

重启终端使用，以上。