A quick one today. Setting up a new machine is always fun, and I tend to use Homebrew to manage what is installed. I've always found that to be a solution with diminishing returns, as it's easy to lose track of what's been installed over time.

The usual tool for this has been brew list, which will show you everything installed via Homebrew. The output of ths really does list everything installed, not just the things you've requested. For example, maybe I want to install foo, so I type:

$ brew install foo

I then have a look at what's installed and get:

$ brew list  
foo     bar     baz

Where did bar and baz come from? They're required for foo to work, so Homebrew installed them for me. Nice. Weeks later I decide foo isn't for me, so I get rid of it:

$ brew uninstall foo  
$ brew list
bar     baz

Huh? What gives? Homebrew hasn't uninstalled the dependencies. This is actually expected behaviour, as maybe I'm using bar or baz on their own. Uninstalling foo doesn't tell Homebrew whether I still need the dependencies or not, so it plays it safe.

The point is that brew list tells me what's installed, not what I installed. To keep track of this, I use Ansible to manage what's installed via brew, so at any time I can see what I've requested. It's not perfect though (as I can still use brew install at any point). I'd given up on keeping solid track of what I'd installed on my machine over time.

Until today, that is. Today I learned about brew leaves. Yes people, I'm here to spread the good word that Homebrew can, in fact, keep track of its installation history:

$ brew install foo
$ brew list
foo     bar     baz
$ brew leaves
foo
$ brew install baz
$ brew leaves
foo     baz

Winning.