CTO and co-founder of Signal Sciences. Author and speaker on software engineering, devops, and security.

Using macOS Homebrew to Install a Specific Version

Because sometimes you don’t want the bleeding edge.

Here's how to install a specific version of a package on macOS using homebrew. While the process isn't automatic, it's also not hard and provides stability.

Why Isn't This Functionality Built-In?

Homebrew used to provide this functionality. If you do search you'll probably find one these methods that no longer works. My guess is the team behind Homebrew removed the functionality since it never worked very well, at scale.

In most Linux distributions, formulas are in separate repositories and can change multiple times before being released with a manual process. The version number is handcrafted and can look like 1.2.3-rc2-ubuntu10.

With homebrew, every formula is in one git repository and every git commit is a potentially a new release for all formula. This makes version numbers hard. For example let's say homebrew did a mass whitespace reformatting of the formula in one commit. Would every package need new version numbers? How would you add them? In a way that is consistent and doesn't have race conditions?

The good news is that getting the exact version you want already is indexed and ready, using git. It's more work, but it's more accurate too.

Find the Hash, Locally

If you are just trying to lock to the latest or a very recently edition, the fastest way is to use:

brew log -p NAME

Then to brew install this version use the raw content from GitHub by replacing _HASH_ and _NAME_ appropriately:

brew install ${BREWURL}/HASH/Formula/NAME.rb

Find the Hash, Remote Edition

Homebrew provided a nice command to pop open a browser window pointing to the change log of a formula:

brew info --github NAME

It takes a few clicks to get the full commit hash. First you'll have to click the History button, find the change you like, then click on another icon to get the full hash. It sounds gross, but in practice it's not too hard.

When GitHub Lets You Down

The Homebrew/homebrew-core repo is very large and using GitHub to look at the commit history for a particular file may timeout. In this case you'll get a "Sorry I'm being lazy, go do it yourself" message. OK then.

Also because it's so big, Homebrew only downloads a bit. However, you can get the full Homebrew history with:

git -C "$(brew --repo homebrew/core)" fetch --unshallow

Then use git to find the entry you want:

git -C "$(brew --repo homebrew/core)" log master -- Formula/phantomjs.rb

As before, craft the URL back to GitHub using the correct hash.

Next Steps

Now that you know how to install a specific version, it would be good time to review how `brew pin` works so you don't lose all your hard work.

macos buildops

© 2018 Nick Galbreath