Break a previous commit into multiple commits

Question

Without creating a branch and doing a bunch of funky work on a new branch, is it possible to break a single commit into a few different commits after it's been committed to the local repository?

Answer 1

From git-rebase manual (SPLITTING COMMITS section)

In interactive mode, you can mark commits with the action "edit". However, this does not necessarily mean that git rebase expects the result of this edit to be exactly one commit. Indeed, you can undo the commit, or you can add other commits. This can be used to split a commit into two:

• Start an interactive rebase with git rebase -i <commit>^, where <commit> is the commit you want to split. In fact, any commit range will do, as long as it contains that commit.

• Mark the commit you want to split with the action "edit".

• When it comes to editing that commit, execute git reset HEAD^. The effect is that the HEAD is rewound by one, and the index follows suit. However, the working tree stays the same.

• Now add the changes to the index that you want to have in the first commit. You can use git add (possibly interactively) or git gui (or both) to do that.

• Commit the now-current index with whatever commit message is appropriate now.

• Repeat the last two steps until your working tree is clean.

• Continue the rebase with git rebase --continue.

Answer 2

git rebase -i will do it.

First, start with a clean working directory: git status should show no pending modifications, deletions, or additions.

To split apart your most recent commit, first:

$ git reset HEAD~

Now commit the pieces individually in the usual way, producing as many commits as you need.

If it was farther back in the tree, then

$ git rebase -i HEAD~3

where 3 is how many commits back it is.

If it was farther back in the tree than you want to count, then

$ git rebase -i 123abcd~

where 123abcd is the SHA1 of the commit you want to split up.

When you get the rebase edit screen, find the commit you want to break apart. At the beginning of that line, replace pick with edit (e for short). Save the buffer and exit. Rebase will now stop just after the commit you want to edit. Then:

$ git reset HEAD~

Commit the pieces individually in the usual way, producing as many commits as you need, then

$ git rebase --continue

Answer 3

Please note there's also git reset --soft HEAD^. It's similar to git reset (which defaults to --mixed) but it retains the index contents. So that if you've added/removed files, you have them in the index already.

Turns out to be very useful in case of giant commits.

Answer 4

Use git rebase --interactive to edit that earlier commit, run git reset HEAD~, and then git add -p to add some, then make a commit, then add some more and make another commit, as many times as you like. When you're done, run git rebase --continue, and you'll have all the split commits earlier in your stack.

Important: Note that you can play around and make all the changes you want, and not have to worry about losing old changes, because you can always run git reflog to find the point in your project that contains the changes you want, (let's call it a8c4ab), and then git reset a8c4ab.

Here's a series of commands to show how it works:

mkdir git-test; cd git-test; git init

now add a file A

vi A

add this line:

one

git commit -am one

then add this line to A:

two

git commit -am two

then add this line to A:

three

git commit -am three

now the file A looks like this:

one
two
three

and our git log looks like the following (well, I use git log --pretty=oneline --pretty="%h %cn %cr ---- %s"

bfb8e46 Rose Perrone 4 seconds ago ---- three
2b613bc Rose Perrone 14 seconds ago ---- two
9aac58f Rose Perrone 24 seconds ago ---- one

Let's say we want to split the second commit, two.

git rebase --interactive HEAD~2

This brings up a message that looks like this:

pick 2b613bc two
pick bfb8e46 three

Change the first pick to an e to edit that commit.

git reset HEAD~

git diff shows us that we just unstaged the commit we made for the second commit:

diff --git a/A b/A
index 5626abf..814f4a4 100644
--- a/A
+++ b/A
@@ -1 +1,2 @@
 one
+two

Let's stage that change, and add "and a third" to that line in file A.

git add .

This is usually the point during an interactive rebase where we would run git rebase --continue, because we usually just want to go back in our stack of commits to edit an earlier commit. But this time, we want to create a new commit. So we'll run git commit -am 'two and a third'. Now we edit file A and add the line two and two thirds.

git add . git commit -am 'two and two thirds' git rebase --continue

We have a conflict with our commit, three, so let's resolve it:

We'll change

one
<<<<<<< HEAD
two and a third
two and two thirds
=======
two
three
>>>>>>> bfb8e46... three

to

one
two and a third
two and two thirds
three

git add .; git rebase --continue

Now our git log -p looks like this:

commit e59ca35bae8360439823d66d459238779e5b4892
Author: Rose Perrone <[e-mail]>
Date:   Sun Jul 7 13:57:00 2013 -0700

    three

diff --git a/A b/A
index 5aef867..dd8fb63 100644
--- a/A
+++ b/A
@@ -1,3 +1,4 @@
 one
 two and a third
 two and two thirds
+three

commit 4a283ba9bf83ef664541b467acdd0bb4d770ab8e
Author: Rose Perrone <[e-mail]>
Date:   Sun Jul 7 14:07:07 2013 -0700

    two and two thirds

diff --git a/A b/A
index 575010a..5aef867 100644
--- a/A
+++ b/A
@@ -1,2 +1,3 @@
 one
 two and a third
+two and two thirds

commit 704d323ca1bc7c45ed8b1714d924adcdc83dfa44
Author: Rose Perrone <[e-mail]>
Date:   Sun Jul 7 14:06:40 2013 -0700

    two and a third

diff --git a/A b/A
index 5626abf..575010a 100644
--- a/A
+++ b/A
@@ -1 +1,2 @@
 one
+two and a third

commit 9aac58f3893488ec643fecab3c85f5a2f481586f
Author: Rose Perrone <[e-mail]>
Date:   Sun Jul 7 13:56:40 2013 -0700

    one

diff --git a/A b/A
new file mode 100644
index 0000000..5626abf
--- /dev/null
+++ b/A
@@ -0,0 +1 @@
+one

Answer 5

Now in the latest TortoiseGit on Windows you can do it very easily.

Open the rebase dialog, configure it, and do the following steps.

• Right-click the commit you want to split and select "Edit" (among pick, squash, delete...).
• Click "Start" to start rebasing.
• Once it arrives to the commit to split, check the "Edit/Split" button and click on "Amend" directly. The commit dialog opens.
  
• Unselect the files you want to put on a separate commit.
• Edit the commit message, and then click "commit".
• Until there are files to commit, the commit dialog will open again and again. When there is no more file to commit, it will still ask you if you want to add one more commit.

Very helpful, thanks TortoiseGit !