How to install an old package version with brew

Sometimes you need to roll back to a previous version of a brew package.
If the brew package maintainers do versioning this is as easy as typing brew install <packageName>@1.2.3.
Often times, there's no versioning system though and the only available version is the latest one.

In previous brew versions you could install a package by directly linking to the GitHub repo that hosts the Formula/<packageName>.rb file.
The repository is usually called homebrew-<packageName> and you can browse through the git commits to find an old Formula/<packageName>.rb file.
For example, you could install an old version of EOSIO.CDT by doing:

brew remove eosio.cdt
brew install https://raw.githubusercontent.com/EOSIO/homebrew-eosio.cdt/d0f0320017315bd5ac69aa1e1ce001c6567af6b3/eosio.cdt.rb

Recent brew versions, however, verschlimmbessert this behavior and the brew police tells you that you're not allowed to do this anymore.

Error: Calling Installation of <packageName> from a GitHub commit URL is disabled! Use 'brew extract ' to stable tap on GitHub instead.

What to do now?

Just do what the error message hints at and use brew extract to stable tap on GitHub.

To save you some time, here's how to do it:

1. You create a local "tap" - which I assume is something like a local brew repository
2. You extract the desired version of the package into this local tap
3. You install your local tap

# use $USER variable to mimick userName/repoName structure
# this does not actually create any git repositories
# 1. create a new tap
brew tap-new $USER/local-<packageName>
# 2. extract into local tap
brew extract --version=1.2.3 <packageName> $USER/local-<packageName>
# 3. run brew install@version as usual
brew install <packageName>@1.2.3

Originally published at https://cmichel.io/how-to-install-an-old-package-version-with-brew/