Installing a specific version of a Homebrew Formula

Thu, Sep 2, 2021

From time to time, I have felt the need to install a specific version of a Homebrew formula. Like the other day, I was investigating whether a particular problem I was facing with Podman was because of a version bump from 2.x to 3.x.

At some point in the past, a way around it was to find the formula file at a particular commit of the Homebrew tap, and directly install it via brew install $URL.

That is no longer supported, for good reason. But the tip provided is pretty terse.

I thought I will just jot down the steps I took to do this the recommended way.

Just for posterity, I have also documented my failed attempt at trying to install it from a specific commit URL. Don’t do that!

Finding the right version of the formula

First, let us find the last 2.x version of the formula I am interested in -podman.

Step into the right repo for the Formula.

$ brew tap-info homebrew/core
homebrew/core: 2 commands, 5786 formulae
/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core (6,417 files, 487.8MB) From:
https://github.com/Homebrew/homebrew-core

$ cd /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core
Shell session

I am interested in the last 2.x version. I used the following command to find the first commit which switched the formula to 3.x.

$ git log -p -G url.*podman -- Formula/podman.rb|grep -e ^commit -e https://github.com/containers/podman/
commit 8070a9ba0b21a0285890544c88f0479a922de809
-  url "https://github.com/containers/podman/archive/v3.3.0.tar.gz"
+  url "https://github.com/containers/podman/archive/v3.3.1.tar.gz"
...
...
commit 623626510d622e64044d1d656e96386cda5cc5b9
-  url "https://github.com/containers/podman/archive/v2.2.1.tar.gz"
+  url "https://github.com/containers/podman/archive/v3.0.0.tar.gz"
^C
Shell session

Ok. So 2.2.1 is the version of the formula I am interested in.

Most homebrew formula follow the same version as upstream. If that is not the case for your formula, you will have to use a different search string in the git command.

Installing the RIGHT way

Create a local tap for storing the formula.

I have made it formula specific (local-podman). But if you tend to do this often for multiple formulas, you can probably name it more generically. To re-emphasize, it doesn’t need to be named after the formula.
```
# Create a local tap for storing the formula
$ brew tap-new $USER/local-podman
```
Shell session

Actually create the copy of the formula at the specific version. brew does all the hard work for you! Look at how it automatically found out the last git commit of the formula when the formula version was what you wanted.

$ brew extract --version=2.2.1 podman $USER/local-podman
==> Searching repository history
==> Writing formula for podman from revision e2c833d to:
/usr/local/Homebrew/Library/Taps/sandipb/homebrew-local-podman/Formula/podman@2.2.1.rb
Shell session

Now your formula will appear in your brew search to be installed the usual way.

$ brew search /podman/
==> Formulae
podman                                    sandipb/local-podman/podman@2.2.1

If you meant "podman" specifically:
It was migrated from homebrew/cask to homebrew/core.

$ HOMEBREW_NO_AUTO_UPDATE=1 brew install sandipb/local-podman/podman@2.2.1
Shell session

I had an unique case though. For some reason though, the checksum in that commit of the formula was broken.

$ HOMEBREW_NO_AUTO_UPDATE=1 brew install sandipb/local-podman/podman@2.2.1
...
Error: SHA256 mismatch
Expected: bd86b181251e2308cb52f18410fb52d89df7f130cecf0298bbf9a848fe7daf60
  Actual: 3212bad60d945c1169b27da03959f36d92d1d8964645c701a5a82a89118e96d1
Shell session

I found out the actual checksum from the official repository, edited the formula to update it and then it installed properly. Perhaps the change in checksum was worth an investigation. It was too late in the night to do that. 😄

$ curl -Ls https://github.com/containers/podman/archive/refs/tags/v2.2.1.tar.gz | sha256sum
3212bad60d945c1169b27da03959f36d92d1d8964645c701a5a82a89118e96d1  -

$ brew edit podman@2.2.1
# ... changed checksum of archive

$ HOMEBREW_NO_AUTO_UPDATE=1 brew install podman@2.2.1

SUCCESS!
Shell session

Installing the WRONG way

As mentioned before, I used the following command to find the first commit which switched the formula to 3.x.

$ git log -p -G url.*podman -- Formula/podman.rb|grep -e ^commit -e https://github.com/containers/podman/
commit 8070a9ba0b21a0285890544c88f0479a922de809
-  url "https://github.com/containers/podman/archive/v3.3.0.tar.gz"
+  url "https://github.com/containers/podman/archive/v3.3.1.tar.gz"
...
...
commit 623626510d622e64044d1d656e96386cda5cc5b9
-  url "https://github.com/containers/podman/archive/v2.2.1.tar.gz"
+  url "https://github.com/containers/podman/archive/v3.0.0.tar.gz"
^C
Shell session

Find the commit previous to this which changed the formula.

$ git log -n 1 623626510d622e64044d1d656e96386cda5cc5b9^ -- Formula/podman.rb
commit e2c833d326c45d9aaf4e26af6dd8b2f31564dc04
Author: Rylan Polster <rslpolster@gmail.com>
Date:   Wed Feb 3 00:13:48 2021 -0500

    formulae: use new bottle syntax
Shell session

So, I found out that e2c833d326c45d9aaf4e26af6dd8b2f31564dc04 is that last update to the formula which had the 2.x version. Now to install this.

$ FORMULA_URL="https://raw.githubusercontent.com/Homebrew/homebrew-core/e2c833d326c45d9aaf4e26af6dd8b2f31564dc04/Formula/podman.rb"

$ HOMEBREW_NO_AUTO_UPDATE=1  brew install $FORMULA_URL
Traceback (most recent call last):
        9: from /usr/local/Homebrew/Library/Homebrew/brew.rb:129:in `<main>'
        8: from /usr/local/Homebrew/Library/Homebrew/cmd/install.rb:131:in `install'
        7: from /usr/local/Homebrew/Library/Homebrew/cli/parser.rb:308:in `parse'
        6: from /usr/local/Homebrew/Library/Homebrew/cli/parser.rb:629:in `formulae'
        5: from /usr/local/Homebrew/Library/Homebrew/cli/parser.rb:629:in `map'
        4: from /usr/local/Homebrew/Library/Homebrew/cli/parser.rb:633:in `block in formulae'
        3: from /usr/local/Homebrew/Library/Homebrew/formulary.rb:414:in `factory'
        2: from /usr/local/Homebrew/Library/Homebrew/formulary.rb:180:in `get_formula'
        1: from /usr/local/Homebrew/Library/Homebrew/formulary.rb:185:in `klass'
/usr/local/Homebrew/Library/Homebrew/formulary.rb:277:in `load_file': Invalid usage: Installation of podman from a GitHub commit URL is unsupported! `brew extract podman` to a stable tap on GitHub instead. (UsageError)
Shell session

Wtf! Frantic web search ensues.

#homebrew

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