Brew outdated notification

brew-outdated-notification.zsh

# brew outdated notification
BREW_OUTDATED_CHECK_TIME=$(cat ~/.brew-outdated-check-time 2>/dev/null)
if [[ -z "${BREW_OUTDATED_CHECK_TIME}" || $(($BREW_OUTDATED_CHECK_TIME + 64800)) -le $(date +%s) ]]; then
  date +%s >| ~/.brew-outdated-check-time
  echo "Checking outdated brew formulae..."
  if [[ -n "${BREW_OUTDATED_CHECK_TIME}" ]]; then
    echo "It was previously checked on $(date -r $BREW_OUTDATED_CHECK_TIME)"
  fi
  brew update --quiet
  outdated=$(brew outdated --quiet)
  pinned=$(brew list --pinned)

  # Remove pinned formulae from the list of outdated formulae
  outdated=$(comm -1 -3 <(echo "${pinned}") <(echo "${outdated}"))

  if [[ -n "${outdated}" ]]; then
    # join lines together with ", " and remove possible trailing comma character
    outdated=$(perl -pe 's/\n/, /g' <(echo "${outdated}") | sed 's/, $//g')
    printf "The following formulae are outdated:\n${outdated}\n"
  else
    echo "No outdated formulae"
  fi
fi