Brew Concepts
Internal
Overview
Homebrew is a package management system for Mac. All applications installed with Homebrew are linked from /usr/local/bin which usually takes precedence over /usr/bin:/bin:/usr/sbin:/sbin, where system utilities are installed. For example, if bash is installed with Homebrew, it'll be usually the newest one and take precedence over the one that comes with the system in /bin/bash.
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. The directory where a specific formula is located can be displayed with:
Brew_Operations#formula <formula-name>
The formulae that have already been applied to the system can be listed with:
brew list
An application that has never been installed on the system can be installed with:
brew install <formula-name>
and it can be updated with:
brew update <formula-name>
Common Formulate
bash
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/bash.rb
Custom Formulae
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
Tap
A tap is a Git repository of formulae and other commands.
Keg
A keg is the installation prefix of a formula. 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