How can I downgrade Homebrew to an older version? - homebrew

Question

Currently I have the latest version 2.2.17, I want to downgrade to version 2.2.12.
Brew does not have a downgrade option, just an upgrade. Is the process to uninstall brew and re-install it again?

Answer 1

If you used the normal installation way via the install script:
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"
Then take a look at the brew install script (it has its own repo).
It downloads the actual Homebrew repo to /usr/local/Homebrew.
...
HOMEBREW_PREFIX="/usr/local"
HOMEBREW_REPOSITORY="/usr/local/Homebrew"
...
BREW_REPO="https://github.com/Homebrew/brew"
...
ohai "Downloading and installing Homebrew..."
(
cd "${HOMEBREW_REPOSITORY}" >/dev/null || return
# "git remote add" will fail if the remote is defined in the global config
execute "git" "config" "remote.origin.url" "${BREW_REPO}"
execute "git" "config" "remote.origin.fetch" "+refs/heads/*:refs/remotes/origin/*"
...
execute "ln" "-sf" "${HOMEBREW_REPOSITORY}/bin/brew" "${HOMEBREW_PREFIX}/bin/brew"
...
}
...
==> This script will install:
/usr/local/bin/brew
/usr/local/share/doc/homebrew
/usr/local/share/man/man1/brew.1
/usr/local/share/zsh/site-functions/_brew
/usr/local/etc/bash_completion.d/brew
/usr/local/Homebrew
...
The script installs the latest copy of the Homebrew repo. So the answer to "Is the process to uninstall brew and re-install it again?" would be a "NO". Instead, install it first normally, and then after, go over to /usr/local/Homebrew and checkout the version you want.
~$ cd /usr/local/Homebrew
Homebrew$ brew --version
Homebrew 2.3.0
Homebrew/homebrew-core (git revision d41d92; last commit 2020-05-29)
Homebrew$ git fetch --tags
Homebrew$ git checkout 2.2.12
Note: switching to '2.2.12'.
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.
If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:
git switch -c <new-branch-name>
Or undo this operation with:
git switch -
Turn off this advice by setting config variable advice.detachedHead to false
HEAD is now at 2ae26808a Merge pull request #7301 from Bo98/cmake-sdkroot
Homebrew$ brew --version
Homebrew 2.2.12
Homebrew$ cd /usr/local/bin
bin$ ./brew --version
Homebrew 2.2.12
Homebrew/homebrew-core (git revision d41d92; last commit 2020-05-29)
I recommend doing a brew doctor after just to make sure everything's still OK.
Then, unfortunately, Homebrew always auto-updates itself every time you install something. So it will always update the repo at /usr/local/Homebrew up again to the latest version. You can disable that by exporting HOMEBREW_NO_AUTO_UPDATE as mentioned here https://github.com/Homebrew/brew/issues/1670.
~$ export HOMEBREW_NO_AUTO_UPDATE=1
~$ brew install python#3.8
You'll need to create an alias or auto-export that env var to your bash_profile (or whatever is the equivalent for the terminal you use), so that it takes effect every time you use brew.