From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christian Couder <chriscool@tuxfamily.org>
Subject: Re: combine git repo historically
Date: Sun, 11 Oct 2009 12:11:55 +0200
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References: <20091009012254.GA3980@debian.b2j> <200910110436.52653.chriscool@tuxfamily.org> <20091011040659.GB9021@debian.b2j>
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Cc: Johannes Sixt <j.sixt@viscovery.net>, git <git@vger.kernel.org>
To: bill lam <cbill.lam@gmail.com>
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On Sunday 11 October 2009, bill lam wrote:
> On Sun, 11 Oct 2009, Christian Couder wrote:
> > $ git checkout -b repo1-branch1 remote/repo1/branch1
> > $ git checkout N -- .
> > ...
> > If everything is ok then you can use:
> >
> > $ git replace N HEAD
>
> Thanks for detail instruction, I tested it ok except that when trying
> to checkout it reported an error
>
>   $ git checkout -b repo1-branch1 remote/oldjproject/master
>   fatal: git checkout: updating paths is incompatible with switching
> branches. Did you intend to checkout 'remote/oldjproject/master' which
> can not be resolved as commit?
>
> but it ran ok by omitting that 'remote/'
> $ git checkout -b repo1-branch1 oldjproject/master
>
> Does it need to purge the file system tree before
>   git checkout N -- .
>
> so that there will be no artifact leaved by M?

Yeah, perhaps, I forgot that there could be some files added and other files 
removed between M and N.

If you remove everything (except the .git directory of course), then doing:

$ git checkout N -- .
$ git add .
$ export GIT_AUTHOR_NAME=<author name of commit N>
$ export GIT_AUTHOR_EMAIL=<author email of commit N>
$ export GIT_AUTHOR_DATE=<date of commit N>
$ git commit

should do the trick if I am not missing something which may very well be the 
case.

So perhaps it is easier to use Jakub's suggestion instead.

> I found that it is necessary to do a
>    git reset --hard (original HEAD)
>
> to complete the story. Is it correct?

Yes, you should go back to your orginal branch at the end.

Regards,
Christian.