From: Linus Torvalds <torvalds@osdl.org>
Date: Tue, 22 Nov 2005 05:23:45 GMT
Subject: Re: index manipulation -- how?
Message-ID: <Pine.LNX.4.64.0511212113080.13959@g5.osdl.org>
In-Reply-To: <20051122050337.46450.qmail@web31808.mail.mud.yahoo.com>



On Mon, 21 Nov 2005, Luben Tuikov wrote:
> 
> How do I reverse a _single_ "git-update-index" operation?
> Be it --add or just an update.

An "add" is easy enough to undo: just do a

	git-update-index --force-remove filename

which will remove the entry from the index even if the file on your 
filesystem still remains (so you can "git add" it later when you do want 
to commit it).

For a file that you had in your old index, but you've updated (either mode 
or SHA1), you need to figure out what the old mode/sha1 was. USUALLY this 
would be just the state that you still have in your HEAD tree, but if 
you want to go back to something else, you'd need to figure out what that 
was.

If it's the "last commit" state (ie just your HEAD state), then do

	git-ls-tree HEAD filename

which will show you the info, and then you do

	git-update-index --cacheinfo <mode> <sha1> filename

from that state.

You could obviously script something like "git-downdate-index":

	#!/bin/sh
	filename="$1"
	tree_info=$(git-ls-tree HEAD -- "$filename")
	if [ -z "$tree_info" ]; then
		git-update-index --force-remove -- "$filename"
	else
		echo "$tree_info" | while read mode type sha1 name; do
			git-update-index --cacheinfo "$mode" "$sha1" "$filename"
		done
	fi

but the above is totally untested, and "git-downdate-index" is a really 
sucky name too, so you'd need to rename it and test whether it does what 
you want.

Hmm?

		Linus