GitHub: How to fork a public repository as a subdirectory in a private repository?

Question

My project is currently hosted in a private repository. I'm looking to introduce a dependency to a third party library hosted in a public repository on GitHub. How can I fork the library so that it becomes a subdirectory in my project, but I can still sync from the trunk branch of that library?

Answer 1

This is called submodule and is described in details at http://git-scm.com/book/en/Git-Tools-Submodules

Answer 2

This sequence would get you set up:

cd <my-project-dir>
git submodule add <github repository> <my-third-party-dir>   # -b <branch> optionally
git submodule init
git submodule update

At this point you've got my-third-party-dir populated with a particular commit (a detached head). Your project will have two changes.

git add .gitmodules <my-third-party-dir>
git commit -m 'Added <repository> as a submodule'