Homebrew: Remove a Formula and Its Unused Dependencies

1 min read

brew uninstall removes only the formula you name. Here is how to clean up the dependencies it pulled in, and why the built-in command is safer than the shell one-liner.

Large formulae pull in a lot of dependencies. At the time of writing, ffmpeg depended on more than 30 other formulae, many with dependencies of their own. brew uninstall ffmpeg removes ffmpeg and leaves all of them behind.

brew info ffmpeg
# ==> Dependencies
# Build: nasm, pkg-config
# Required: aom, dav1d, fontconfig, freetype, frei0r, gnutls, lame, libass, ...

The short answer

Since Homebrew 2.5.9 (late 2020), the built-in way is:

brew uninstall ffmpeg
brew autoremove --dry-run   # review what would be removed
brew autoremove

autoremove uninstalls formulae that were installed only as dependencies and that nothing else installed still needs. It reads Homebrew's own record of what you asked for (installed_on_request) and what came along as a dependency, so it won't remove a dependency that another formula still uses, or one you installed directly.

The older one-liner

Before autoremove, the common approach looked like this. I originally published it in this post:

pkg=ffmpeg
brew uninstall "$pkg"
brew uninstall $(join <(brew leaves) <(brew deps "$pkg"))

How it works:

  1. brew deps "$pkg" lists the formula's dependencies.
  2. brew leaves lists installed formulae that no other installed formula depends on.
  3. join keeps the names in both lists: dependencies of pkg that are now leaves, so nothing else needs them.

It works for simple cases but has sharp edges:

  • It can remove things you meant to keep. brew leaves includes formulae you installed on purpose. If you installed pkg-config yourself, it is still a leaf and still a dependency of ffmpeg, so it gets removed. autoremove knows the difference.
  • It only cleans up one level. Sub-dependencies become leaves only after their parents are removed, so you have to run it repeatedly.
  • join assumes sorted input. Both commands happen to print sorted output today; nothing guarantees it.

Use brew autoremove, and pass --dry-run first whenever you're unsure.