So you have a nice big project that you’ve been working on for a while and you are at a state where you think it will be nice to split a part of the project. This can be to either create it as a library to use it with other projects or just maintain it independantly.

There are two steps involved:

• Splitting out the subpath from the repository and creating a new repository from it.
• Using this new git repository we’ve created in the main repository so that we can continue working.

Let’s tackle them one at a time.

Splitting a subpath into a new repository

I’m assuming that we’re interested in keeping the git history - else, you can simply just copy out the directory into a new folder and init it as a new repository.

Using git filter-branch

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git filter-branch --prune=empty --subdirectory-filter my-api -- --all

The -- --all is to ensure that we filter all the branches in the repository.

Next, you simply add new remotes and push your repository there.

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git remote add my-new-remote git@github.com:adhipg/new-remote.git
git push --all

Side note: You’ll have to clone the original repository again.

Using git subtree

git subtree is a new git command that recently was added into git. Using it to create the new repository is simple enough:

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git subtree split --prefix my-api --branch my-api-repo

Now the my-api-repo branch consists of just the contents from my-api and all the relevant commits. This can now be used to push to a new remote:

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git push git@github.com:adhipg/new-remote.git split:master

Merging the subpath back into the original repository

We use git subtree from earlier for this.

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git subtree add --prefix my-api --squash git@github.com:adhipg/new-remote.git master

The --squash here implies that we just want to create a merge commit - else, we’ll end up with duplicate commits in the history.

Up Next: Maintaining both the repositories simultaneously.