Tap the keg:

  brew tap nhemsley/homebrew-env https://github.com/nhemsley/homebrew-env.git

Install:

 brew install homebrew-env

Cache the shellenv:

  brew env recache

Put this in ~/.bashrc OR ~/.profile etc.

. $(brew env source-file)

Show the shellenv

  brew env shellenv

Edit $HOMEBREW_PREFIX/etc/brew-env/presets.yaml to create/change environment scripts.

They key is the same as the brew installed package name.

Not hard.

PR's welcome for presets.yaml updates, and anything else.