---
title: brew leaves
teaser: |
  How to use Homebrew's `brew leaves` command
  to find programs you can safely uninstall.
tags: osx
author: Gabe Berke-Williams
published_on: 2014-02-11
---

No, it's not about tea. We're continuing our [rundown of lesser-known Homebrew
features][osx] with `brew leaves`. Let's check the `man brew` page:

    leaves   Show installed formulae that are not dependencies of another installed formula.

Or, in more computer science-y terms, it shows you the leaves of the Homebrew
dependency graph.

## When to use it

`brew leaves` shows you programs that you can safely uninstall. If you want to
clean house, just run `brew leaves` and happily uninstall:

    $ brew leaves | wc -l
    45
    $ brew leaves
    ...
    leiningen
    ...
    pngcrush
    ...

We have 45 leaves. We haven't used `leiningen` in a while, and forgot `pngcrush`
was even installed. Let's uninstall:

    $ brew uninstall pngcrush leiningen
    $ brew leaves | wc -l
    43

We now have 2 fewer leaves. If `pngcrush` or `leiningen` were the only things
that depended on a third package `foo`, then uninstalling those two packages would
make `foo` a new leaf, since now nothing depends on `foo`.

## Easily create a Brewfile

[Brewfiles][Brewfile] are an easy way to install frequently-used Homebrew
packages on a new machine. We can easily create a Brewfile using `brew leaves`:

    $ brew leaves | sed 's/^/install /' > Brewfile
    $ wc -l Brewfile
    42
    $ head -3 Brewfile
    install aspell
    install bison
    install colordiff

Now all 42 packages we depend on are neatly listed. One possible concern is that
a package will be left out - for example, we use `rbenv` but it's not in the
Brewfile. This is because we also have `rbenv-gem-rehash` installed, which
depends on `rbenv`, making `rbenv` not a leaf. Since `rbenv-gem-rehash` depends
on `rbenv`, installing it will also install `rbenv`. We're safe.

## What's next

You can learn how to [start and stop background services in Homebrew][services].
You can also take a deep dive into [graph theory].

[osx]: https://thoughtbot.com/blog/tags/osx
[Brewfile]: https://thoughtbot.com/blog/brewfile-a-gemfile-but-for-homebrew
[services]: https://thoughtbot.com/blog/starting-and-stopping-background-services-with-homebrew
[graph theory]: http://diestel-graph-theory.com