It's an external command for Homebrew. It provides installation caveat descriptions for Homebrew packages.

Although the script's name is brew-caveats.rb, Homebrew external commands work in such a way that you invoke it as brew caveats. (It functions exactly like a sub-command built into Homebrew.)

If you already know the name of a package, and you want to see a bit about it, that's easy:

$ brew caveats zsh
==> zsh: Caveats
Add the following to your zshrc to access the online help:
    unalias run-help
    autoload run-help
    HELPDIR=/usr/local/share/zsh/helpfiles

You can install brew caveats in two ways.

1. Tap this repository and install via brew itself.
2. Install manually.

For the first method, do the following:

brew tap rafaelgarrido/homebrew-caveats && brew install brew-caveats

For the second method clone or download this repository. Then simply put the file brew-caveats.rb anywhere in your $PATH. For example:

mv brew-caveats.rb ~/bin

Leave the name as is if you follow this method. Homebrew knows how to find it.

Once you've installed via either method, you can use the command as described above.