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Git Submodule Guide

Sometimes you may have to keep third party libraries included in you project up to date in an easy way. Submodules in Git makes this as simple as a pimple.

Adding a Submodule to a Git Repository

First, lets add the third party repository as a submodule to a sub folder in our own repository:

~/code > git submodule add git@mygithost:project.git lib/folder
Cloning into lib/folder...
remote: Counting objects: 448, done.
remote: Compressing objects: 100% (444/444), done.
remote: Total 448 (delta 290), reused 0 (delta 0)
Receiving objects: 100% (448/448), 493.84 KiB | 322 KiB/s, done.
Resolving deltas: 100% (290/290), done.

Now, lets see what this did to our repository:

~/code > git status
# On branch master
#
# Initial commit
#
# Changes to be committed:
#   (use "git rm --cached <file>..." to unstage)
#
#new file:   .gitmodules
#new file:   lib/folder

The .gitmodules file basically tells Git to keep track of lib/folder as a git submodule. Add those files and get on with it:

git add . && git commit -m "Submodule added"

Using and Updating a Git Submodule

When cloning a repository with submodules in it for the first time, the folders where the submodules live are empty. In order to get the latest source you can initialize the submodule:

git submodule init

And then update it:

git submodule update

Voila!

You can look at submodules as its own repositories inside yours. And as submodules updated this way are headless, we can make sure to pull from a specific branch in our submodule (in this case, master):

cd lib/folder
git checkout master
git pull

Commit those changes and we’re done!