How to split a git repository while preserving subdirectories?

Question

What I want is similar to this question. However, I want the directory that is split into a separate repo to remain a subdirectory in that repo:

I have this:

Answer 1

This is what I ended up doing to solve this issue when I had it myself:

git filter-branch --index-filter \
'git ls-tree --name-only --full-tree $GIT_COMMIT | \
 grep -v "^directory-to-keep$" | \
 sed -e "s/^/\"/g" -e "s/$/\"/g" | \
 xargs git rm --cached -r -f --ignore-unmatch \
' \
--prune-empty -- --all

The solution is based on Jefromi’s answer and on Detach (move) subdirectory into separate Git repository plus many comments here on SO.

The reason why Jefromi’s solution did not work for me was, that I had files and folders in my repo whose names contained special characters (mostly spaces). Additionally git rm complained about unmatched files (resolved with --ignore-unmatch).

You can keep the filtering agnostic to the directory not being in the repo’s root or being moved around:

grep --invert-match "^.*directory-to-keep$"

And finally, you can use this to filter out a fixed subset of files or directories:

egrep --invert-match "^(.*file-or-directory-to-keep-1$|.*file-or-directory-to-keep-2$|…)"

To clean up afterwards you can use these commands:

$ git reset --hard
$ git show-ref refs/original/* --hash | xargs -n 1 git update-ref -d
$ git reflog expire --expire=now --all
$ git gc --aggressive --prune=now