Git submodulesEdit

Workflows

Adding a new submodule

One typical workflow: public project, public submodules.

• you want anonymous users to be able to clone the public project and its submodules
• but you want to be able to push changes from within the submodules

# add submodule to project, using public URL
git submodule add git://git.example.com/project.git project

# update your config file
git submodule init

# edit config to use private URL
vim .git/config

# checkout submodules, they will use the private URL
git submodule update

Now you have push access set up via the private URL in your own copy of the repository, but if an anonymous user clones they'll just get the standard public/anonymous (read-only) access.

Note that if you have already checked out the submodules before you configure the private URL you'll need to go into the submodule's .git/config and tweak the URL there as well in order for your git push to work.

Updating a submodule

cd foo_submodule

# after making some changes in the submodule (by fetching/merging, or editing/committing)
# we want to record those changes in the superproject
cd ..
git add foo_submodule

# we want our commit message to include a summary of the changes made in the submodule
# note the "-e" switch allows us to review/edit the commit message before, er, committing to it
git diff --submodule --cached -- foo_submodule | git commit -s -e -F -

# or alternatively (slightly different format)
git submodule summary foo_submodule | git commit -s -e -F -

This is a pattern I employ fairly commonly, so I have an alias set up for it:

git config --global alias.smc '!git submodule summary -- $1 > ~/tmp/COMMIT_MSG && git commit -s -t ~/tmp/COMMIT_MSG'

Note that I ended up using a temporary file rather than a pipe because Vim tends to complain and I haven't had time to investigate why yet.