How can I copy a directory from one git repository to another, preserving history?

Question

I know that I can create a new repository out of a directory of a git repository. See here: https://help.github.com/articles/splitting-a-subfolder-out-into-a-new-repository/

However, how can I copy a directory from one repository to a new directory of another completely different repository, while keeping history of that directory?

Update: is it possible for that history to show up with git log?

Answer 1

You could do this with git filter-branch. Basically you'd want to:

1. Split out the subpath in the first project into a new repository, using the link you've already found.
2. Push it to the second project's remote on a unique branch.

3. Fetch that branch into the second repository, then use git filter-branch to index-filter it into the correct subdirectory:

   git filter-branch --index-filter '
       git ls-files -sz | 
       perl -0pe "s{\t}{\tnewsubdir/}" |
       GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
           git update-index --clear -z --index-info &&
           mv "$GIT_INDEX_FILE.new" "$GIT_INDEX_FILE"
   ' HEAD
   

4. Finally, checkout the master branch of the second project (or whatever branch you're using), then merge in the newly-filtered branch.

Really not too awful an operation, all told. As AlexanderGladysh notes in the comments, you could also use a subtree merging strategy in the place of steps 3 and 4.