Detach many subdirectories into a new, separate Git repository

Question

This question is based on Detach subdirectory into separate Git repository

Instead of detaching a single subdirectory, I want to detach a couple. For example, my current directory tree looks like this:

/apps
  /AAA
  /BBB
  /CCC
/libs
  /XXX
  /YYY
  /ZZZ

And I would like this instead:

/apps
  /AAA
/libs
  /XXX

The --subdirectory-filter argument to git filter-branch won't work because it gets rid of everything except for the given directory the first time it's run. I thought using the --index-filter argument for all unwanted files would work (albeit tedious), but if I try running it more than once, I get the following message:

Cannot create a new backup.
A previous backup already exists in refs/original/
Force overwriting the backup with -f

Any ideas? TIA

Answer 1

Instead of having to deal with a subshell and using ext glob (as kynan suggested), try this much simpler approach:

git filter-branch --index-filter 'git rm --cached -qr --ignore-unmatch -- . && git reset -q $GIT_COMMIT -- apps/AAA libs/XXX' --prune-empty -- --all

As mentioned by void.pointer's comment, this will remove everything except apps/AAA and libs/XXX from current repository.

Prune empty merge commits

This leaves behind lots of empty merges. These can be removed by another pass as described by raphinesse in his answer:

git filter-branch --prune-empty --parent-filter \
'sed "s/-p //g" | xargs -r git show-branch --independent | sed "s/\</-p /g"'

⚠️ Warning: The above must use GNU version of sed and xargs otherwise it would remove all commits as xargs fails. brew install gnu-sed findutils and then use gsed and gxargs:

git filter-branch --prune-empty --parent-filter \
'gsed "s/-p //g" | gxargs git show-branch --independent | gsed "s/\</-p /g"'