Metamix is a tool to update and build multiple projects. Why would you want this? Well it's really handy to get a local copy of the documentation of many projects with a single command.

The basic idea behind metamix is that you tell it you want to have the most recent version of dynamo and the 0.1 release of ecto and it goes and fetches the git repositories for dynamo and ecto and then checks out the master branch of dynamo and the 0.1 tag for ecto and builds those using mix (hence the name "metamix", it's a layer above mix).

Metamix needs to be told which projects there are. This is easy to do, for example for dynamo just create a file named "dynamo.metamix" with the following content:

{ "name": "dynamo",
  "description": "A web framework for Elixir",
  "git": "https://github.com/elixir-lang/dynamo"
}

The name has to be consistent with the filename. Metamix work with unique names for each project. This is a design choice to encourage people not to have projects with clashing names. For forks it's easy to create a separate metamix file for the fork (for example I could name my own fork of ex_doc ex_doc-pminten).

The description is optional, but it allows metamix to print a list of available projects and what they are for and also comes in handy when generating the big list of documentation.

The git field should contain something you can pass to git clone. Typically this will be https://github.com/USER/REPO.

Make sure the directory containing the metamix file is in the METAMIX_PATH environment variable. It's possible for a repository managed by metamix to be in the METAMIX_PATH. In fact this is an excellent way to implement a global list of projects.