Update a submodule to the latest commit

Question

I have a project A which is a library and it is used in a project B.

Both projects A and B have a separate repository on github BUT inside B we have a submodule of A

Answer 1

If you update a submodule and commit to it, you need to go to the containing, or higher level repo and add the change there.

git status

will show something like:

modified:
   some/path/to/your/submodule

The fact that the submodule is out of sync can also be seen with

git submodule

the output will show:

+afafaffa232452362634243523 some/path/to/your/submodule

The plus indicates that the your submodule is pointing ahead of where the top repo expects it to point to.

simply add this change:

git add some/path/to/your/submodule

and commit it:

git commit -m "referenced newer version of my submodule"

When you push up your changes, make sure you push up the change in the submodule first and then push the reference change in the outer repo. This way people that update will always be able to successfully run

git submodule update

More info on submodules can be found here http://progit.org/book/ch6-6.html.