[macos] Uninstall / remove a Homebrew package including all its dependencies

I have a Homebrew formula that I wish to uninstall/remove along with all its dependencies, skipping packages whom other packages depend upon (a.k.a. Cascading package removal in Package manager parlance).

e.g. Uninstall package a which depends on packages b & c, where package d also depends on package c. The result should uninstall both a & b, skipping c.

How can I do that?

There must be a way to uninstall a package without leaving unnecessary junk behind.

The answer of @jfmercer must be modified slightly to work with current brew, because the output of brew missing has changed:

brew deps [FORMULA] | xargs brew remove --ignore-dependencies && brew missing | cut -f1 -d: | xargs brew install

Save the following script as brew-purge

#!/bin/bash
#:Usage: brew purge formula
#: 
#:Removes the package and all dependancies.
#: 
#: 
PKG="$1"
if [ -z "$PKG" ];then
   brew purge --help
   exit 1
fi
brew rm $PKG
[ $? -ne 0 ] && exit 1
while brew rm $(join <(brew leaves) <(brew deps $PKG)) 2>/dev/null
  do :
done
echo Package $PKG and its dependancies have been removed.
exit 0

Now install it with the following command

sudo install brew-purge /usr/local/bin

Now run it

brew purge package

Example using gpg

$ brew purge gpg
Uninstalling /usr/local/Cellar/gnupg/2.2.13... (134 files, 11.0MB)
Uninstalling /usr/local/Cellar/adns/1.5.1... (14 files, 597.5KB)
Uninstalling /usr/local/Cellar/gnutls/3.6.6... (1,200 files, 8.9MB)
Uninstalling /usr/local/Cellar/libgcrypt/1.8.4... (21 files, 2.6MB)
Uninstalling /usr/local/Cellar/libksba/1.3.5... (14 files, 344.2KB)
Uninstalling /usr/local/Cellar/libusb/1.0.22... (29 files, 508KB)
Uninstalling /usr/local/Cellar/npth/1.6... (11 files, 71.7KB)
Uninstalling /usr/local/Cellar/pinentry/1.1.0_1... (12 files, 263.9KB)
Uninstalling /usr/local/Cellar/libassuan/2.5.3... (16 files, 444.2KB)
Uninstalling /usr/local/Cellar/libtasn1/4.13... (59 files, 436KB)
Uninstalling /usr/local/Cellar/libunistring/0.9.10... (54 files, 4.4MB)
Uninstalling /usr/local/Cellar/nettle/3.4.1... (85 files, 2MB)
Uninstalling /usr/local/Cellar/p11-kit/0.23.15... (63 files, 2.9MB)
Uninstalling /usr/local/Cellar/gmp/6.1.2_2... (18 files, 3.1MB)
Uninstalling /usr/local/Cellar/libffi/3.2.1... (16 files, 296.8KB)
Uninstalling /usr/local/Cellar/libgpg-error/1.35... (27 files, 854.8KB)
Package gpg and its dependancies have been removed.
$ 

The goal here is to remove the given package and its dependencies without breaking another package's dependencies. I use this command:

brew deps [FORMULA] | xargs brew remove --ignore-dependencies && brew missing | xargs brew install

Note: Edited to reflect @alphadogg's helpful comment.

Based on @jfmercer answer (corrections needed more than a comment).

Remove package's dependencies (does not remove package):

brew deps [FORMULA] | xargs brew remove --ignore-dependencies

Remove package:

brew remove [FORMULA]

Reinstall missing libraries:

brew missing | cut -d: -f2 | sort | uniq | xargs brew install

Tested uninstalling meld after discovering MeldMerge releases.

brew rmtree doesn't work at all. From the links on that issue I found rmrec which actually does work. God knows why brew doesn't have this as a native command.

brew tap ggpeti/rmrec
brew rmrec pkgname

You can just use a UNIX pipe for this

brew deps [FORMULA] | xargs brew rm

A More-Complete Bourne Shell Function

There are a number of good answers already, but some are out of date and none of them are entirely complete. In particular, most of them will remove dependencies but still leave it up to you to remove the originally-targeted formula afterwards. The posted one-liners can also be tedious to work with if you want to uninstall more than one formula at a time.

Here is a Bourne-compatible shell function (without any known Bashisms) that takes a list of formulae, removes each one's dependencies, removes all copies of the formula itself, and then reinstalls any missing dependencies.

unbrew () {
    local formula
    for formula in "$@"; do
        brew deps "$formula" |
        xargs brew uninstall --ignore-dependencies --force
        brew uninstall --force "$formula"
    done
    brew missing | cut -f2 -d: | sort -u | xargs brew install
}

It was tested on Homebrew 1.7.4.

Caveats

This works on all standard formulae that I tested. It does not presently handle casks, but neither will it complain loudly if you attempt to unbrew a cask with the same name as a standard formula (e.g. MacVim).

Using this answer requires that you create and maintain a file that contains the package names you want installed on your system. If you don't have one already, use the following command and delete the package names what you don't want to keep installed.

brew leaves > brew_packages

Then you can remove all installed, but unwanted packages and any unnecessary dependencies by running the following command

brew_clean brew_packages

brew_clean is available here: https://gist.github.com/cskeeters/10ff1295bca93808213d

This script gets all of the packages you specified in brew_packages and all of their dependancies and compares them against the output of brew list and finally removes the unwanted packages after verifying this list with the user.

At this point if you want to remove package a, you simply remove it from the brew_packages file then re-run brew_clean brew_packages. It will remove b, but not c.

Other answers didn't work for me, but this did (in fish shell):

brew remove <package>
for p in (brew deps <package>)
    brew remove $p
end

Because brew remove $p fails when some other package depends on p.