Efficiently detecting paths that differ from each other only in case

Hi,

I'm writing a Git hook, for a bare central repo, to reject pushes of paths that differ from existing tracked paths only by letter case.

So, for example, if the following path is tracked in the repo:

foo/bar.py

Commits adding any of the following paths would be rejected:

Foo/bar.py foo/Bar.py fOO/BAR.py

Etc. I know how to do it by listing paths with ls-files, but my repo contains many thousands of files, so I was wondering if there was a more efficient way than for every commit:

1. Get a list of all paths in the repo from ls-files.
2. Lowercase all paths.
3. Check for repeats.

Thanks, D