How can I have linked dependencies in a git repo?

You can do this with submodules in git. In your repository, do:

git submodule add path_to_repo path_where_you_want_it

So, if the library's repository had a URL of git://github.com/example/some_lib.git and you wanted it at lib/some_lib in your project, you'd enter:

git submodule add git://github.com/example/some_lib.git lib/some_lib

Note that this needs to be done from the top-level directory in your repository. So don't cd into the directory where you're putting it first.

After you add a submodule, or whenever someone does a fresh checkout of your repository, you'll need to do:

git submodule initgit submodule update

And then all submodules you've added will be checked out at the same revision you have.

When you want to update to a newer version of one of the libraries, cd into the submodule and pull:

cd lib/some_libgit pull

Then, when you do a git status you should see lib/somelib listed in the modified section. Add that file, commit, and you're up to date. When a collaborator pulls that commit into their repository, they'll see lib/somelib as modified until they run git submodule update again.