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Splitting a commit with rebase -i and keeping a commit message

Subject: Splitting a commit with rebase -i and keeping a commit message

## tl;dr

4 messages between Apr 17, 2013 and Apr 17, 2013.

replies: 3people: 3as markdown or json

Tim Chase· Apr 17, 2013, 01:38 UTC · lore

I asked this on IRC and played with some of their ideas, but struck out with anything satisfying. I walked through [1] with the following setup:

  git init foo
  cd foo
  touch a.txt b.txt
  git add a.txt b.txt
  git commit -m "Initial checkin"
  echo "Modify A" >> a.txt
  git commit -am "Modified A"
  echo "Modify B" >> b.txt
  git commit -am "Modified B"
  echo "Modify A2" >> a.txt
  echo "Modify B2" >> b.txt
  git commit -am "Modified B"
  git commit -am "Long-bodied commit comment about b.txt changes"
  # whoops, just wanted B
  git rebase -i HEAD^^
  # change the "Added b.txt..." commit to "edit"
  git reset HEAD^  # pull the changes out of the pending commit
  git add a.txt
  git commit -m "Tweaked a.txt"
  git add b.txt
  git commit ${MAGIC_HERE}
  git rebase --continue

I haven't been able to figure out a good way to keep the "long-bodied commit comment" for the final commit where the ${MAGIC_HERE} is. Is there a right/easy way to go about pulling in the commit-message from the commit the rebase is transplanting?

-tkc

[1] http://git-scm.com/book/en/Git-Tools-Rewriting-History#Splitting-a-Commit

David Aguilar· Apr 17, 2013, 02:29 UTC · re: Tim Chase · lore

Re: Splitting a commit with rebase -i and keeping a commit message

Taking a wild guess here...
On Tue, Apr 16, 2013 at 6:38 PM, Tim Chase <git@tim.thechases.com> wrote:
Show 18 quoted lines
> I asked this on IRC and played with some of their ideas, but struck
> out with anything satisfying.  I walked through [1] with the
> following setup:
>
>   git init foo
>   cd foo
>   touch a.txt b.txt
>   git add a.txt b.txt
>   git commit -m "Initial checkin"
>   echo "Modify A" >> a.txt
>   git commit -am "Modified A"
>   echo "Modify B" >> b.txt
>   git commit -am "Modified B"
>   echo "Modify A2" >> a.txt
>   echo "Modify B2" >> b.txt
>   git commit -am "Modified B"
>   git commit -am "Long-bodied commit comment about b.txt changes"
>   # whoops, just wanted B
Save the commit's ID here so that we can reuse its message later:
    orig_commit=$(git rev-parse HEAD)
Show 7 quoted lines
>   git rebase -i HEAD^^
>   # change the "Added b.txt..." commit to "edit"
>   git reset HEAD^  # pull the changes out of the pending commit
>   git add a.txt
>   git commit -m "Tweaked a.txt"
>   git add b.txt
>   git commit ${MAGIC_HERE}
...reuse the commit message by passing the "-c" option to "git commit":
    git commit --reset-author -c $orig_commit
This will give you a chance to further edit the message in your editor.
Show 6 quoted lines
>   git rebase --continue
>
> I haven't been able to figure out a good way to keep the "long-bodied
> commit comment" for the final commit where the ${MAGIC_HERE} is.  Is
> there a right/easy way to go about pulling in the commit-message from
> the commit the rebase is transplanting?

This is pretty much what the commands above do. They save the commit ID so that we can reuse the message later.

HTH, -- David

Tim Chase· Apr 17, 2013, 03:04 UTC · re: David Aguilar · lore

Re: Splitting a commit with rebase -i and keeping a commit message

On 2013-04-16 19:29, David Aguilar wrote:
Show 21 quoted lines
> On Tue, Apr 16, 2013 at 6:38 PM, Tim Chase <git@tim.thechases.com>
> wrote:
> >   git commit -am "Long-bodied commit comment about b.txt changes"
> >   # whoops, just wanted B
> 
> Save the commit's ID here so that we can reuse its message later:
> 
>     orig_commit=$(git rev-parse HEAD)
> 
> >   git rebase -i HEAD^^
> >   # change the "Added b.txt..." commit to "edit"
> >   git reset HEAD^  # pull the changes out of the pending commit
> >   git add a.txt
> >   git commit -m "Tweaked a.txt"
> >   git add b.txt
> >   git commit ${MAGIC_HERE}
> 
> ...reuse the commit message by passing the "-c" option to "git
> commit":
> 
>     git commit --reset-author -c $orig_commit

Wild guess or not, using -c worked great. With the appropriate section of the docs now in hand, I discovered that it could even be simplified to just

  git commit -c ORIG_HEAD [...]
as rebase stashes that information away for me already as "ORIG_HEAD".
Thanks!
-tkc
Johannes Sixt· Apr 17, 2013, 05:55 UTC · re: Tim Chase · lore

Re: Splitting a commit with rebase -i and keeping a commit message

Am 4/17/2013 3:38, schrieb Tim Chase:
Show 20 quoted lines
> I asked this on IRC and played with some of their ideas, but struck
> out with anything satisfying.  I walked through [1] with the
> following setup:
> 
>   git init foo
>   cd foo
>   touch a.txt b.txt
>   git add a.txt b.txt
>   git commit -m "Initial checkin"
>   echo "Modify A" >> a.txt
>   git commit -am "Modified A"
>   echo "Modify B" >> b.txt
>   git commit -am "Modified B"
>   echo "Modify A2" >> a.txt
>   echo "Modify B2" >> b.txt
>   git commit -am "Modified B"
>   git commit -am "Long-bodied commit comment about b.txt changes"
>   # whoops, just wanted B
>   git rebase -i HEAD^^
>   # change the "Added b.txt..." commit to "edit"
    # and duplicate the instruction line
    git checkout HEAD^ b.txt # undo b.txt
    git commit --amend -m "Tweaked a.txt"
    git rebase --continue
    # in real world cases, you are likely to see conflicts here
    # when the commit is applied a second time,
    # but not in this toy example
    git rebase --continue
-- Hannes

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