From: Jeff King <peff@peff.net>
Date: Tue, 12 May 2009 16:07:49 GMT
Subject: Re: How to create a new commit with the content of some commit?
Message-ID: <20090512160749.GA29566@coredump.intra.peff.net>
In-Reply-To: <46dff0320905120735l501dcaf4ia8197d24b7684cfe@mail.gmail.com>

On Tue, May 12, 2009 at 10:35:30PM +0800, Ping Yin wrote:

> a----b
>  \----c
> 
> Given the graph above, I want to create a commit b1 on top of c, where
> b1 and b have the same content. i.e.
> 
> a----b
>  \----c----b1    ( content(b) == content(b1) )
> 
> If there are no untracked files in the working directory, i can do
> 
> git checkout b
> git reset c
> git add .
> git commit -m "the copy of b"
> 
> Is there any simpler way? And if there are untracked files in the
> working directory, how to do it?

You can just munge the index directly, and skip the working tree
entirely:

  rm .git/index
  git read-tree b
  git commit -m 'the copy of b'

You would probably want to "git checkout -f" afterwards to update the
working tree with what's in the index.

You can also do it without even touching the index by using the commit
plumbing:

  echo 'copy of b' >message
  tree=`git rev-parse b^{tree}`
  commit=`git commit-tree $tree -p c <message`
  git update-ref c $commit

-Peff