Git Tracks the Submodule’s State

Get the experimental branch#

Since your alicelib submodule is a straightforward clone of the remote alicelib origin, you have the master branch and the origin’s experimental branch:

1   cd alicelib2   git branch -a -vv

You are on the master branch (current HEAD location is indicated with a *), which is mapped to remotes/origin/master.

References Will Be Different
The refs (e.g., ff75b7f) will be different in your output.

You do not have an experimental branch locally. However, if you check out a branch that does not exist locally but does exist remotely, Git will assume you want to track that remote branch.

3   git checkout experimental4   git branch -a -vv

More Than One Remote With The Same Branch?
If more than one remote has the same name, Git will not perform this matching. In that case, you would have to run the full command that follows.

Alternatively, you could track a completely different branch if you specify it:

5   git checkout -b alicemaster --track origin/master

This is, assuming it’s the origin’s master branch that you want to track.

Now that you’ve checked out and tracked the remote experimental branch in your submodule, a change has taken place in bob_repo. If you return to bob_repo’s root folder and run git diff, you will see that the subproject commit of alicelib has changed:

6   cd ..7   git diff

The commit reference now matches the experimental reference.

Note that “bob_repo” tracks the specific commit and not the remote branch. This means that changes to “alicelib” in the origin repository are not automatically tracked within bob_repo’s submodule. This is a crucial difference with submodules; they are static in that they are pointed at a specific point in the history until you move it on.

You want to commit this change to the submodule:

8   git commit -am 'alicelib moved to experimental'

Alice Makes a Change#

Alice now spots a bug in her experimental branch that she wants to fix:

9   cd ../alicelib10  git checkout experimental11  echo 'D' >> file112  git commit -am 'D - a fix added'

There is a mismatch between alicelib’s experimental branch and bob_repo’s experimental branch.

13  cd ../bob_repo/alicelib14  git status

git status reports that bob_repo’s alicelib is up-to-date with origin/experimental. Remember that origin/experimental is the locally-stored representation of alicelib’s experimental branch. Since you have not contacted alicelib to see if there are any updates, this is still the case.

To get the latest changes, you can perform a fetch and merge or save time by running a git pull, which does both:

15  git pull

Warning!
Generally, I would advise against editing repositories that are checked out as submodules until you are more experienced with Git. You may quickly find yourself in a detached HEAD state and confused about what you’ve done.