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Homebrew, like Git, supports external commands. This lets you create new commands that can be run like:

$ brew mycommand --option1 --option3 formula

without modifying Homebrew's internals.


External commands come in two flavors: Ruby commands and shell scripts.

In both cases, the command file should be chmod +x (executable) and live somewhere in $PATH.

Internally, Homebrew finds commands with which(1).


An external command extcmd implemented as a Ruby command should be named brew-extcmd.rb. The command is executed by doing a require on the full pathname. As the command is required, it has full access to the Homebrew "environment", i.e. all global variables and modules that any internal command has access to.

The command may Kernel.exit with a status code if it needs to; if it doesn't explicitly exit then Homebrew will return 0.


A shell script for an command named extcmd should be named brew-extcmd. This file will be run via exec with some Homebrew variables set as environmental variables, and passed any additional command-line arguments.

Variable Description
HOMEBREW_CACHE Where Homebrew caches downloaded tarballs to, typically ~/Library/Caches/Homebrew.
HOMEBREW_CELLAR The location of the Homebrew Cellar, where software is staged, by default /usr/local/Cellar.
HOMEBREW_LIBRARY_PATH The directory containing Homebrew’s own application code.
HOMEBREW_PREFIX Where Homebrew installs software to, by default /usr/local.
HOMEBREW_REPOSITORY If installed from a Git clone, the repo directory (i.e., where Homebrew’s .git directory lives).

Note that the script itself can use any suitable shebang (#!) line, so an external “shell script” can be written for sh, bash, Ruby, or anything else.


Some example external commands ship with Homebrew and are enabled by default. You can list them by doing

$ ls `brew --repository`/Library/Contributions/cmd

Some commands in the example commands directory are documented in the brew(1) man page. For documentation on the missing, server, and which commands, see man brew.

bottle <formulae>

Build a binary package (bottle) from the keg(s) of <formulae>.


Like brew list --versions, but lists only formulae with multiple installed versions.

graph [brew-deps-options]

Generate a GraphViz DOT file from the Homebrew dependency graph. Options given here are passed on to brew deps.

grep [grep-options]

Grep through Homebrew formulae in HOMEBREW_REPOSITORY/Library/Formula. Options given here are passed on to grep(1).

man [--verbose|-v] [--link|-l] [--server|-s]

[Re]generate man pages for Homebrew using ronn(1).

If --verbose is passed, run man brew after generating man pages.

If --link is passed, symlink generated man pages to HOMEBREW_PREFIX/share/man. This is useful when Homebrew is not installed directly into /usr/local.

If --server is passed, start the ronn(1) test server.

mirror-check <formula...>

Cycle through mirror lists for each formula, attempt a download and validate MD5 sums.

missing [<formulae>]

Check the given <formulae> for missing dependencies.

If no <formulae> are given, check all installed brews.

pull <URLish> [--install]

Get a patch from a GitHub commit or pull request and apply it to Homebrew. <URLish> may be the URL of a GitHub commit or pull request, or the issue number of a pull request.

If --install is passed, installs any formulae added or modified by the patch.


Import all formulae one by one. This is useful for testing new functionality across all formulae, or to check all formulae for errors.


Start a local web app that lets you browse available formulae, similar to gem server. Requires sinatra.

switch <formula> <version>

Switch between installed versions of <formula>. If you have multiple versions of a formula installed, the standard brew link command will fail. switch tries to unlink all versions from HOMEBREW_PREFIX, then [re]links the requested version.

unpack [--patch] [--destdir=path/to/extract/in] <formulae>

Unpack the source code of <formulae> for inspection. Formulae archives will be extracted to subdirectories inside the current working directory or a directory specified by --destdir. If the --patch option is supplied, patches will also be downloaded and applied.

which [<formulae>]

List versions of installed brews.

If <formulae> are given, only list versions for the specified brews.


These commands have been contributed by Homebrew users but are not included in the main Homebrew repository, nor are they installed by the installer script. You can install them manually, as outlined above.

NOTE: They are largely untested, and as always, be careful about running untested code on your machine.


Install .app and other "Drag to install" packages from Homebrew.

Install using:

$ brew install phinze/cask/brew-cask


Get short descriptions for Homebrew formulae or search formulae by description:

You can install manually or using brew tap:

$ brew install telemachus/desc/brew-desc

brew-gem and brew-pip

Install any gem pip package into a self-contained Homebrew cellar location,

Note: These can also be installed with brew install brew-gem and brew install brew-pip


Get Growl notifications for Homebrew


Scrapes a formula's homepage to get more information:


Does brew update followed by brew outdated:


Does a rebase on "brew update" instead of a merge:


Simple support to start formulae using launchctl, has out of the box support for any formula which defines startup_plist (e.g. mysql, postgres, redis u.v.m.):


Homebrew Wiki:

brew(1), which(1), grep(1), ronn(1)

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