maintain

Not shallow clone!!!

Error: 
  homebrew-core is a shallow clone.
To `brew update`, first run:
  git -C /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow

This command may take a few minutes to run due to the large size of the repository.
This restriction has been made on GitHub's request because updating shallow
clones is an extremely expensive operation due to the tree layout and traffic of
Homebrew/homebrew-core and Homebrew/homebrew-cask. We don't do this for you
automatically to avoid repeatedly performing an expensive unshallow operation in
CI systems (which should instead be fixed to not use shallow clones). Sorry for
the inconvenience!

pre-compiled(Bottle)

brew prefers pre-compiled binaries but will compile from source in some cases.

这些预编译的二进制文件，被称为bottle，它们存放在:

• https://github.com/Homebrew/homebrew-core/packages.

brew目标在于预编译一切能编译的。(We aim to bottle everything)

只要有机会提供预编译文件，它就会提供，除非遇到以下情况:

1. Options were passed to the install command, i.e. brew install <formula> will use a bottled version of the formula, but brew install --enable-bar will trigger a source build. The --build-from-source option is invoked.
2. No bottle is available for the machine’s currently running OS version. (Bottles for macOS are generated only for supported macOS versions.)
3. Homebrew is installed to a prefix other than the default (although some bottles support this).

Cask

brew cask is an extension to brew that allows management of graphical applications through the Cask project.

Homebrew Cask extends Homebrew and brings its elegance, simplicity, and speed to OS X applications and large binaries alike.

Cask deals with a mixture of software and licences. The software I work on is covered by a commercial licence and available via cask.

Cask offers a way to command line manage the installation of graphical applications.

See brew cask issue #7002 about the project's focus on predictability and how that affects the use of pre-compiled binaries or source.