Brew Concepts
Internal
Formula
A formula is a package definition written in Ruby. Homebrew comes with a good amount of existing formulae, and they are stored as Ruby files in the default tap named "homebrew": /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/<package-name>.rb.
New formulae can be can be created. Instructions are available here: https://docs.brew.sh/Formula-Cookbook. The sequence is:
brew create <URL>
where <URL> is a zip or tar file, installed with
brew install <formula>
and debugged with:
brew install --debug --verbose <formula>
Formula API: http://www.rubydoc.info/github/Homebrew/brew/master/Formula
Common Formulate
bash
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/bash.rb
Tap
A tap is a Git repository of formulae and other commands.
Keg
A keg is the installation prefix of a formula, and it can be logically thought of as an installed application (name + version). The corresponding directories are stored in cellar.
Example:
/usr/local/Cellar/foo/0.1
Cellar
The directory where all kegs are stored:
/usr/local/Cellar