Extreme git filter-branch: keep only one or a few files

filter.sh

# Based on <http://git.661346.n2.nabble.com/Remove-all-files-except-a-few-files-using-filter-branch-td7567155.html>
# for most of it (the index filter part) and on this SO answer for how to get rid of the many meaningless commits now:
# <http://stackoverflow.com/a/5326065/265522>

git filter-branch --index-filter "git rm --cached -qr -- . && git reset -q $GIT_COMMIT -- THEFILEYOUWANTTOKEEP" # --prune-empty
git filter-branch --commit-filter 'git_commit_non_empty_tree "$@"'

I find this script only keep files but not the history.