1. Add the following lines to your ~/.bashrc, ~/.zshrc, etc. file(s):

(IMPORTANT: replace <path> with the absolute path to this Github project repo)

(UPDATE_HOMEBREW_DAYS defaults to 7 days, if unset)

# ---------
# Homebrew Package Auto-Upgrade Config
# ---------

# Change how often to auto-update Homebrew (in days)
export UPDATE_HOMEBREW_DAYS=7

# Path to Homebrew auto-update installation (Github project repo)
export UPDATE_HOMEBREW_PATH=<path>

# Homebrew auto-update script
source $UPDATE_HOMEBREW_PATH/homebrew-updater.sh

This Homebrew package auto-upgrade tool also stores a .brew-last-update file in your user's home directory, which contains a record of when the user was last prompted to run the Homebrew auto-upgrade tool.

2. You can edit the homebrew_updater() function, at line 14 in homebrew-updater.sh, to define your own Homebrew package auto-upgrade steps.

Each time your ~/.bashrc, ~/.zshrc, etc. file(s) are loaded, simple info and warning logs are sent to debug.log, in this Git project repo.