Downgrade / switch gnupg version in homebrew and pin it

switch-gnupg.sh

#!/bin/bash -e
#-------------------------------------------------------------------------------------
# Summary: Executes commands to...
#   * Check/output currently installed version of gnupg
#   * Change into the brew repo/install directory
#   * Find the git commit-id of the specified version of gnupg
#   * git branch/switch to the commit-id
#   * replace the brew installed version with the specified version (and pin it)
#   * clean up the branch, switch back to master, and remove cached files
#   * Check/output the newly installed version of gnupg
#
# Usage:
#   switch-gnupg.sh [version-to-install]
# Example:
#   switch-gnupg.sh 2.4.0
#-------------------------------------------------------------------------------------

# Reference: https://gist.github.com/talal/1b8d0c11338dc9ab79b2386309828894
# Indirect Reference: https://zoltanaltfatter.com/2017/09/07/Install-a-specific-version-of-formula-with-homebrew/
# Reference: https://github.com/Homebrew/homebrew-bundle/issues/1062

if [ $# -eq 0 ]; then
    echo "Usage: $0 [version of gnupg to install - e.g. '1.20.4_1']"
    kill -INT $$
fi

# show what is installed currently via brew
brew list

# this does not work any more...
#  brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/d1f410dcd8426cf7ce1afb7614319c127d821ed8/Formula/gnupg.rb
# Note: look into this more: brew install kubectx && brew install asdf
#    See: https://faun.pub/switch-easily-between-multiple-kubernetes-version-on-macos-9d61b9bc8287

# show the path to the gpg command currently executed by default
which gpg

# see what version of gnupg is currently linked/installed
# Note: || true just ignores errors if the default server config can't connect or something like that.
gpg --version || true

# see what versions of gnupg _can_ be installed using brew
# Note: when this script was written only one previous version (1.22) was available as a Formula
# and it wasn't "previous enough" to fall within the +/- 1 version required by k8s for use with
# the cluster version (1.20)
brew search gnupg

pushd $(brew --repo homebrew/core)

echo "Target gnupg version number: $1"
# Assuming the only regex-special characters in the version number will be ".", just escape those using sed
VERSION_ARG_AS_REGEX=$(echo $1 | sed "s/\./\\\./g")
echo "VERSION_ARG_AS_REGEX: $VERSION_ARG_AS_REGEX"

# Extract the commit id matching the specified version from the git commit logs.
COMMIT_ID_FOR_VERSION=$(git --no-pager log --max-count=1 --grep="$VERSION_ARG_AS_REGEX bottle" Formula/gnupg.rb |grep ^commit | cut -d ' ' -f2)
echo "COMMIT_ID_FOR_VERSION: $COMMIT_ID_FOR_VERSION"

# In case this was already done for a different version of the tool... unpin it first.
brew unpin gnupg

# Switching versions requires a full delete/uninstall or the brew install command
# will skip over download/install and just say to brew link instead, which doesn't
# have the desired result of switching to a totally different binary.
# TODO: Find a combination of unlink, link, etc. that will avoid re-downloading.
brew uninstall --ignore-dependencies gnupg

git checkout -b gnupg-$1 $COMMIT_ID_FOR_VERSION

export HOMEBREW_NO_AUTO_UPDATE=1

brew install --formula Formula/gnupg.rb

unset HOMEBREW_NO_AUTO_UPDATE

# tell bash to clear its cache of executable files
# See: https://unix.stackexchange.com/questions/5609/how-do-i-clear-bashs-cache-of-paths-to-executables
# ATTENTION: This is something you might not know bash does, but it's worth being aware of it.
hash -r

brew pin gnupg

brew info gnupg

# verify that the new version of gnupg is linked/installed
gpg --version || true

# Restore brew's git local clone status to master branch so it functions normally for other stuff again
git checkout master
git branch -d gnupg-$1

# Clean up cached files related to installing the specific version of gnupg
brew cleanup gnupg

popd