how to extract folders with history with git

Sometimes at the end of life of a project, one of its sub-project will fly on its own and will have its own lifecycle.

Thus, you will need to extract the folder of the sub-project.

Will a simple copy/paste work? Not so fast, because we will lose the git history of the sub-project.

Git is an awesome tool which has a “magical” command.

For example, we have a projet called foobar with the following tree:

foobar
  |_ foo
  |_ bar
  |_ someotherfolder

If I want to extract the 2 sub-folders foo and bar with their history, we just need to execute the following command:

git filter-branch --tag-name-filter cat --index-filter 'git rm --cached -qr --ignore-unmatch -- . && git reset -q $GIT_COMMIT -- foo bar' --prune-empty -- --all

--tag-name-filter cat: option to fetch the history for their tags
--: separate the filter-branch options from the revision options
--all: re-write all branches and tags