Re: index manipulation -- how?

Luben Tuikov [off-list ref] writes:

How do I reverse a _single_ "git-update-index" operation?
Be it --add or just an update.

Reverting working tree files are "git checkout HEAD the-file"
(both index and working tree file from the head commit) or "git
checkout -- the-file" (working tree file from the index), but I
do not think there is a prepackaged way to revert only a single
index path offhand.

        git-ls-tree HEAD the-file |
        sed -e 's/^\([0-7]*\) [^ ]* \(.*\)/\1 \2/' |
        git-update-index --index-info

should work.

I think changing update-index --index-info so that you can lose
the sed in between without breaking its other usage (it reads
from git-apply --index-info, which does not say " blob " which
is what the sed is stripping out) is a worthwhile thing to do.