Intro/Rant

Homebrew

Homebrew is one of the most famous package manager for macOS (and Linux!).

Why?

There are numerous post which will tell you all sorts of reasons (ref #1, #2, #3), but for simplicity sake, most tutorial for CLI stuff has brew as a pre-requisite!

This blogpost is not discussing about brew’s popular status against developers, but rather some inconvenience bug (or feature?) which occurs when you need specific (non-latest) version of a binary!

These steps are sourced from multiple brilliant sources (ref #1, #2, #3)

How-to steps

Note: for simplicity sake, this example uses conftest package, in which the latest was 0.44.0 at the time of writing, and target version to downgrade is 0.34.0

  1. Check current version of conftest

     conftest -v 

 Conftest: 0.44.1
 OPA: 0.54.0

  2. Since our target version of conftest is 0.34.0, which is lower than current version 0.44.1, we need to look for latest commit at homebrew git repository - to find latest commit which contains version 0.34.0 - how?

    By performing brew info conftest

     brew info conftest

 ==> conftest: stable 0.44.1 (bottled), HEAD
 Test your configuration files using Open Policy Agent
 https://www.conftest.dev/
 /opt/homebrew/Cellar/conftest/0.44.1 (8 files, 52.8MB) *
   Poured from bottle using the formulae.brew.sh API on 2023-07-19 at 17:31:19
 From: https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/conftest.rb
 License: Apache-2.0
 ==> Dependencies
 Build: go ✔
 ==> Options
 --HEAD
         Install HEAD version
 ==> Caveats
 zsh completions have been installed to:
   /opt/homebrew/share/zsh/site-functions
 ==> Analytics
 install: 0 (30 days), 0 (90 days), 0 (365 days)
 install-on-request: 0 (30 days), 0 (90 days), 0 (365 days)
 build-error: 0 (30 days)

    Take note of link shown in From :, which is now located at https://github.com/Homebrew/homebrew-core/blob/HEAD/Formula/conftest.rb

  3. Find target version you want by using brew log conftest command. This will show git log of the brew formula selected in your favorite text editor (in CLI!) - sample output from my screen:

     commit d6d316a90b1dd580babbb7ec70b226911ab14528
 Author: BrewTestBot <1589480+BrewTestBot@users.noreply.github.com>
 Date:   Sun Jul 9 05:34:05 2023 +0000
    
     conftest: update 0.44.1 bottle.
    
 commit 37b987c8b2d4279f570024addab68cee6c5b4e70
 Author: Rui Chen <rui@chenrui.dev>
 Date:   Sun Jul 9 00:42:40 2023 -0400
    
     conftest 0.44.1
    
 commit acf20dffb41cfc9188044951f9b16cea53c7e14b
 Author: BrewTestBot <1589480+BrewTestBot@users.noreply.github.com>
 Date:   Wed Jun 7 07:50:52 2023 +0000

  4. Look for target version that you want - in this example, find 0.34.0 and take note of the commit SHA:

     commit 93cc2fb873fcf4a71811d3fc34d61d58ef0b79cf
 Author: BrewTestBot <1589480+BrewTestBot@users.noreply.github.com>
 Date:   Tue Aug 2 08:05:32 2022 +0000
    
     conftest: update 0.34.0 bottle.
    
 commit debe60730f13de0d655737f776c722335d0ad073
 Author: BrewTestBot <1589480+BrewTestBot@users.noreply.github.com>
 Date:   Tue Aug 2 05:27:51 2022 +0000
    
     conftest 0.34.0
    
     Closes #107097.

    Since there were two commit, pick the first one(93cc2fb873fcf4a71811d3fc34d61d58ef0b79cf)!

  5. Replace HEAD in the URL from Step (2) with commit SHA from Step (4). In this example, the combined URL is: https://github.com/Homebrew/homebrew-core/blob/93cc2fb873fcf4a71811d3fc34d61d58ef0b79cf/Formula/conftest.rb

  6. Modify URL at Step (5) from github.com to raw.githubusercontent.com, and remove /blob so you can download the .rb file for further use! Final URL: https://raw.githubusercontent.com/Homebrew/homebrew-core/93cc2fb873fcf4a71811d3fc34d61d58ef0b79cf/Formula/conftest.rb

  7. Uninstall current package from brew

     brew uninstall conftest

 Uninstalling /opt/homebrew/Cellar/conftest/0.44.1... (8 files, 52.8MB)

  8. Download raw .rb file from Step 6 locally and brew install from the locally downloaded file File name must not be changed, or brew install will report error!

     curl https://raw.githubusercontent.com/Homebrew/homebrew-core/93cc2fb873fcf4a71811d3fc34d61d58ef0b79cf/Formula/conftest.rb > conftest.rb
 brew install conftest.rb

 ==> Downloading https://formulae.brew.sh/api/formula.jws.json
 #################################################################################################################################### 100.0%
 Error: Failed to load cask: conftest.rb
 Cask 'conftest' is unreadable: wrong constant name #<Class:0x000000010b07d080>
 Warning: Treating conftest.rb as a formula.
 ==> Fetching conftest
 ==> Downloading https://ghcr.io/v2/homebrew/core/conftest/manifests/0.34.0
 Already downloaded: /Users/chris/Library/Caches/Homebrew/downloads/4b20beaf460f5ab5e37cc63c5c3d16a970b866186fcf9993353e0722cc5b18a0--conftest-0.34.0.bottle_manifest.json
 ==> Downloading https://ghcr.io/v2/homebrew/core/conftest/blobs/sha256:e701a40383b9e466d6fb2fc4a767fdbfa36cdd6c4f864bf9b34328b36b037b17
 #################################################################################################################################### 100.0%
 Warning: conftest 0.44.1 is available and more recent than version 0.34.0.
 ==> Pouring conftest--0.34.0.arm64_monterey.bottle.tar.gz
 ==> Downloading https://formulae.brew.sh/api/cask.jws.json
 #################################################################################################################################### 100.0%
 ==> Caveats
 zsh completions have been installed to:
   /opt/homebrew/share/zsh/site-functions
 ==> Summary
 🍺  /opt/homebrew/Cellar/conftest/0.34.0: 8 files, 47.2MB
 ==> Running `brew cleanup conftest`...
 Disable this behaviour by setting HOMEBREW_NO_INSTALL_CLEANUP.
 Hide these hints with HOMEBREW_NO_ENV_HINTS (see `man brew`).
 Removing: /Users/chris/Library/Caches/Homebrew/conftest--0.34.0... (20.9MB)

  9. Check that conftest is now using version 0.34.0, and pin the version to prevent auto-update from brew install or brew update

     conftest -v 
 Conftest: 0.34.0
 OPA: 0.43.0

 brew pin conftest

  10. Done! Enjoy your pinned package~