Provide a detailed description of the proposed feature

There's certain commands (e.g. brew update, brew doctor) that will read/evaluate all formulae and all casks from all tapped taps.

What is the motivation for the feature?

The current behaviour is unexpected and (I'd argue) undesirable. I consider it expected behaviour to read the formula/casks that are already installed with commands such as brew update/brew doctor but not every formula/cask in every tap.

HOMEBREW_UPDATE_REPORT_ONLY_INSTALLED already does some of this for brew update. I use it and it improves the output (and potentially speed).

How will the feature be relevant to at least 90% of Homebrew users?

Improved security and speed of those commands.

What alternatives to the feature have been considered?

• The status quo
• Sandboxing (with blocked network access?) all reads (only available on macOS) to improve security