The way we handle boolean environment variables is a bit unfortunate. For example, setting `HOMEBREW_EVAL_ALL=false` actually enables `HOMEBREW_EVAL_ALL`. Let's fix this by deprecating setting boolean environment variables to common false-y values (`false`, `0`, `nil`, `no`, and `off`) so that we can later ignore these false-y values when reading boolean environment variables.
Library
This directory contains all the code run by the official brew command in Homebrew and all formulae (package descriptions) in taps (repositories containing formulae) in Taps subdirectories.