Diverging Branches

Last updated on 2026-03-02 | Edit this page

Overview

Questions

What are diverged branches?
How do I keep my development branch up-to-date with main?
What is merging?
What is rebasing?

Objectives

How to keep a development branch up-to-date using
- git merge
- git rebase
Differences between and when to use merge and rebase.

Diverging Branches

As you and your collaborator(s) work on your repository you may find that changes others have made get merged into the main before you have finished your work. This has in fact just happened, the work to add a Zero Division exception has been merged via a Pull Request, but the work to address the Square Root function hasn’t and is in effect behind the main branch. The following is a representation of the current state, albeit from a single developer.

%%{init: {'theme': 'base', 'gitGraph': {'rotateCommitLabel': true}
         }
}%%
    gitGraph
       accTitle: Simple Git Branches
       accDescr {Diverging branches in python-maths ns-rse/2-square-root is now behind the main branch which has incorporated the changes from ns-rse/1-zero-division.}
       commit id: "0-472f101"
       commit id: "1-51816d6"
       commit id: "2-6769ff2 (base)"
       branch "ns-rse/1-zero-division"
       branch "ns-rse/2-square-root"
       checkout "ns-rse/1-zero-division"
       commit id: "3-8c52dce"
       checkout "ns-rse/2-square-root"
       commit id: "4-8ec389a"
       checkout "ns-rse/1-zero-division"
       commit id: "5-2315fa0"
       checkout "ns-rse/2-square-root"
       commit id: "6-93e787c"
       checkout main
       merge "ns-rse/1-zero-division" id: "7-bc43901" tag: "Merge zero division"
       commit id: "HEAD"

In this example the main branch now includes the commits 3-8c52dce and 5-2315fa0 from the ns-rse/1-zero-division branch as well as the commit 7-bc43901 which was made when the ns-rse/1-zero-division branch was merged in. The ns-rse/2-square-root branch does not contain these commits.

Sometimes this won’t be a problem, the two features/issues are completely independent and have not made changes to the same file. In such cases it is possible to merge the branches into main without any “merge conflicts” because neither have modified the same files in the same location.

That will not always be the case though, sometimes merge conflicts might arise if the second branch is changing the same files in the same place as the first branch. Another scenario might be that whilst work was being done on adding a new feature branch, a critical bug was fixed that the new feature depends on and the changes now in main need incorporating in the feature branch. That is in fact the situation we have with our ns-rse/4-square-root branch, it conflicts with main because of the changes we merged from the ns-rse/3-zero-division branch.

There are two approaches to solving this: merging (git merge) and rebasing (git rebase).

Merging

%%{init: {'theme': 'base', 'gitGraph': {'rotateCommitLabel': true}
         }
}%%
    gitGraph
       accTitle: Diverging Branches
       accDescr {Before - diverged branches in python-maths. The branch ns-rse/2-square-root is now behind the main
       branch which has incorporated the changes from the ns-rse/1-zero-division branch.}
       commit id: "0-472f101"
       commit id: "1-51816d6"
       commit id: "2-6769ff2 (base)"
       branch "ns-rse/1-zero-division"
       branch "ns-rse/2-square-root"
       checkout "ns-rse/1-zero-division"
       commit id: "3-8c52dce"
       checkout "ns-rse/2-square-root"
       commit id: "4-8ec389a"
       checkout "ns-rse/1-zero-division"
       commit id: "5-2315fa0"
       checkout "ns-rse/2-square-root"
       commit id: "6-93e787c"
       checkout main
       merge "ns-rse/1-zero-division" id: "7-bc43901" tag: "v0.1.1"
       commit id: "HEAD"
       checkout "main"

%%{init: {'theme': 'base', 'gitGraph': {'rotateCommitLabel': true}
         }
}%%
    gitGraph
       accTitle: Merging Diverged Branches
       accDescr {After - main, which has already had the work in ns-rse/1-zero-division merged into it, is
       merged into ns-rse/2-square-root. Development is completed on ns-rse/2-square-root and the feature merged
       into main.}
       commit id: "0-472f101"
       commit id: "1-51816d6"
       commit id: "2-6769ff2 (base)"
       branch "ns-rse/1-zero-division"
       branch "ns-rse/2-square-root"
       checkout "ns-rse/1-zero-division"
       commit id: "3-8c52dce"
       checkout "ns-rse/2-square-root"
       commit id: "4-8ec389a"
       checkout "ns-rse/1-zero-division"
       commit id: "5-2315fa0"
       checkout "ns-rse/2-square-root"
       commit id: "6-93e787c"
       checkout main
       merge "ns-rse/1-zero-division" id: "7-bc43901" tag: "v0.1.1"
       commit id: "HEAD"
       checkout "ns-rse/2-square-root"
       merge "main" id: "8-a80cef8" tag: "Merge main"
       commit id: "9-cb839a0"
       commit id: "10-1ae54c3"
       checkout "main"
       merge "ns-rse/2-square-root" id: "11-a8c9932" tag: "v0.1.2"

The syntax of git merge is

BASH

git merge <OPTIONS> <ref>

Where <ref> is one of a commit hash, branch name or tag (both of which are references to commit hashes). There is an option for how the merge is made known as fast-forward. Fast-forward is the default and it is used when a branch is merged with its ancestor which itself has no new commits.

Often though, as in this example, the main branch contains work from someone else’s branch and your feature branch and main have therefore diverged, and we want to incorporate the changes that have been introduced to main into the feature branch that is being worked on.

1. Make a new repository

BASH

cd ~/work/git/hub/ns-rse
mkdir git-merge-test
cd git-merge-test
git init --initial-branch=main
git commit --allow-empty -m "Initial commit"

2. Create `branch1`, add a `README.md` and commit it

BASH

git switch -c branch1
echo -e "# Just a test" > README.md
git add README.md
git commit -m "docs: Adding README.md"
git lol
cat README.md

3. Switch back to `main`

Check the contents of README.md (there is no such file as the it exists on branch1).

BASH

git switch main
cat README.md   # Note that `README.md` does not currently exist on this branch
git lol

4. Create `branch2`, add a `LICENSE` and commit it

BASH

git switch -c branch2
echo -e "YOU CAN DO WHAT YOU WANT WITH THIS CODE" > LICENSE
git add LICENSE
git commit -m "chore: Adding a LICENSE"
git lol
cat LICENSE

5. Merge `branch1` into `main`

Switch back to main and merge branch1 (this is equivalent to merging a Pull Request). The file README.md now exists on the main branch.

BASH

git switch main
git merge branch1
cat README.md
git lol

6. Merge `main`, which now contains `README.md`, into `branch2`

Switch to branch2 which has now diverged as it contains changes of its own and main contains the changes made on branch1. We want to merge the changes on main and “fast-forward” if possible.

BASH

git switch branch2
git merge --ff main # Merge changes merged into main from branch1 into branch2
git lol

*   d914fee - (HEAD -> branch2) Merge branch 'main' into branch2 (2024-03-01 12:02:08 +0000) <Neil
|\
| * 7817070 - (main, branch1) Adding a README.md (2024-03-01 11:57:35 +0000) <Neil Shephard>
* | a14a643 - Adding a LICENSE (2024-03-01 12:00:39 +0000) <Neil Shephard>
|/
* 1bd6bb8 - Initial commit (2024-03-01 11:57:06 +0000) <Neil Shephard>

It might seem strange that commit 7817070 is listed after a14a643 when the README.md was created and committed first but this is just an artefact of how the graph is drawn as the timestamps show.

7. Merge `branch2` into `main`

We now have the changes from branch1 included in branch2 by virtue of having merged main. If we switch back to main we can merge the changes from branch2.

BASH

git switch main
git merge branch2
git lol
*   d914fee - (HEAD -> main, branch2) Merge branch 'main' into branch2 (2024-03-01 12:02:08 +0000) <Neil Shephard>
|\
| * 7817070 - (branch1) Adding a README.md (2024-03-01 11:57:35 +0000) <Neil Shephard>
* | a14a643 - Adding a LICENSE (2024-03-01 12:00:39 +0000) <Neil Shephard>
|/
* 1bd6bb8 - Initial commit (2024-03-01 11:57:06 +0000) <Neil Shephard>
ls -lh
.rw-r--r-- neil neil 40 B Fri Mar 01 11:57:21 LICENSE
.rw-r--r-- neil neil 14 B Fri Mar 01 11:58:03 README.md

8. Delete `branch1` and `branch2`

As we’re done with branch1 and branch2 we can delete them.

BASH

# Delete the two branches
git branch -d branch{1,2}
git lol
*   d914fee - (HEAD -> main) Merge branch 'main' into branch2 (2024-03-01 12:02:08 +0000) <Neil Shephard>
|\
| * 7817070 - Adding a README.md (2024-03-01 11:57:35 +0000) <Neil Shephard>
* | a14a643 - Adding a LICENSE (2024-03-01 12:00:39 +0000) <Neil Shephard>
|/
* 1bd6bb8 - Initial commit (2024-03-01 11:57:06 +0000) <Neil Shephard>

Having used git merge we couldn’t perform a simple fast-forward because the history of main now contained changes that were made on branch1 and so a separate commit (d914fee) was made to merge the main branch into branch2 (commits are denoted by * and so you can see the commits were made on separate branches). We can see from the graph that README.md was added from a separate branches, although after deleting the branches they are no longer shown by name in the output.

Rebasing

Rebasing moves the point at which the branch diverged from its original position to another, in this case the HEAD of the main branch. You are changing the base commit, hence the name git rebase.

%%{init: {'theme': 'base', 'gitGraph': {'rotateCommitLabel': true}
         }
}%%
    gitGraph
       accTitle: Diverged Branches
       accDescr {Before - diverged branches in python-maths. The branch ns-rse/2-square-root is now behind the main
       branch which has incorporated the changes from the ns-rse/1-zero-division branch.}
       commit id: "0-472f101"
       commit id: "1-51816d6"
       commit id: "2-6769ff2 (base)"
       branch "ns-rse/1-zero-division"
       branch "ns-rse/2-square-root"
       checkout "ns-rse/1-zero-division"
       commit id: "3-8c52dce"
       checkout "ns-rse/2-square-root"
       commit id: "4-8ec389a"
       checkout "ns-rse/1-zero-division"
       commit id: "5-2315fa0"
       checkout "ns-rse/2-square-root"
       commit id: "6-93e787c"
       checkout main
       merge "ns-rse/1-zero-division" id: "7-bc43901" tag: "v0.1.1"
       commit id: "HEAD"
       checkout "main"

%%{init: {'theme': 'base', 'gitGraph': {'rotateCommitLabel': true}
         }
}%%
    gitGraph
       accTitle: Rebasing
       accDescr {After - rebase to bring the diverged branch up-to-date with main which includes
       ns-rse/1-zero-division. Two more commits are made and ns-rse/2-square-root is then merged into main.}
       commit id: "0-472f101"
       commit id: "1-51816d6"
       commit id: "2-6769ff2 (base)"
       branch "ns-rse/1-zero-division"
       checkout "ns-rse/1-zero-division"
       commit id: "3-8c52dce"
       checkout "ns-rse/1-zero-division"
       commit id: "5-2315fa0"
       checkout main
       merge "ns-rse/1-zero-division" id: "7-bc43901" tag: "v0.1.1"
       commit tag: "Rebase"
       branch "ns-rse/2-square-root"
       checkout "ns-rse/2-square-root"
       commit id: "4-8ec389a"
       checkout "ns-rse/2-square-root"
       commit id: "6-93e787c"
       commit id: "7-cb839a0"
       commit id: "8-1ae54c3"
       checkout "main"
       merge "ns-rse/2-square-root" id: "9-ba93020" tag: "v0.1.2"

git rebase takes a different approach to bringing branches up-to-date and in effect moves the point at which a branch diverged from main rather than merging the changes in.

1. Make a new repository

BASH

cd ~/work/git/hub/ns-rse
mkdir git-rebase-test
cd git-rebase-test
git init --initial-branch=main
git commit --allow-empty -m "Initial commit"

2. Create `branch1`, add a `README.md` and commit it

BASH

git switch -c branch1
echo -e "# Just a test" > README.md
git add README.md
git commit -m "docs: Adding README.md"

3. Switch back to `main`

As before README.md does not exist on the main branch.

BASH

git switch main
cat README.md   # Note that `README.md` does not currently exist on this branch

4. Create `branch2`, add a `LICENSE` and commit it

BASH

git switch -c branch2
echo -e "YOU CAN DO WHAT YOU WANT WITH THIS CODE" > LICENSE
git add LICENSE
git commit -m "docs: Adding a LICENSE"

5. Merge `branch1` into `main` (equivalent to making a Pull Request)

Switch back to main and merge branch1 (this is equivalent to merging a Pull Request). The file README.md now exists on the main branch.

BASH

git switch main
git merge branch1  # Merge branch1 into main, equivalent to a Pull Request
cat README.md
git lol

6. Rebase `branch2` onto `main` so it includes the `README.md` and the point of divergence is updated

Switch to branch2 which has now diverged as it contains changes of its own and main contains the changes made on branch1. We want to rebase branch2 onto main so that it appears as if branch2 forked after the changes from branch1 were merged.

BASH

git switch branch2
git rebase main # Rebase branch2 onto main
git lol

* 12f5202 - (HEAD -> branch2) Adding a LICENSE (2024-03-01 12:19:12 +0000) <Neil Shephard>
* 4e8e933 - (main, branch1) Adding README.md (2024-03-01 12:18:37 +0000) <Neil Shephard>
* 2459609 - Initial commit (2024-03-01 12:18:37 +0000) <Neil Shephard>

NB The commits here are listed in chronological order because there is no branching.

7. Merge `branch2` into `main`

We now have the changes from branch1 included in branch2 by virtue of having rebased onto main after the changes in branch1 were merged in. If we switch back to main we can merge the changes from branch2.

BASH

git switch main
git merge branch2
git lol

* 12f5202 - (HEAD -> main, branch2) docs: Adding a LICENSE (2024-03-01 12:19:12 +0000) <Neil Shephard>
* 4e8e933 - (branch1) docs: Adding README.md (2024-03-01 12:18:37 +0000) <Neil Shephard>
* 2459609 - Initial commit (2024-03-01 12:18:37 +0000) <Neil Shephard>

8. Delete `branch1` and `branch2`

As we’re done with branch1 and branch2 we can delete them.

BASH

git branch -d branch{1,2}
git lol

* 12f5202 - (HEAD -> main) Adding a LICENSE (2024-03-01 12:19:12 +0000) <Neil Shephard>
* 4e8e933 - Adding README.md (2024-03-01 12:18:37 +0000) <Neil Shephard>
* 2459609 - Initial commit (2024-03-01 12:18:37 +0000) <Neil Shephard>

As you can see the history of the main branch is now linear.

Challenge

Challenge 1: Diverging Branches

In your pairs bring the square-root branch up-to-date and incorporate the changes that have been merged into main from the zero-division branch and then create a Pull Request to merge the updated square-root changes into main on GitHub, review it and merge it.

The person who has been working on the square-root issue/branch will be at the helm for this, but work together to come up with a solution. You can use either of the two strategies git merge or git rebase to do this.

IMPORTANT - You should encounter a “conflict”, please do not try and solve this yet as we will go through how to do this.

%%{init: {'theme': 'base', 'gitGraph': {'rotateCommitLabel': true}
         }
}%%
    gitGraph
       accTitle: Diverged Branches
       accDescr {Diverged Branches.}
       commit id: "0-472f101"
       commit id: "1-51816d6"
       commit id: "2-6769ff2 (base)"
       branch "ns-rse/1-zero-division"
       branch "ns-rse/2-square-root"
       checkout "ns-rse/1-zero-division"
       commit id: "3-8c52dce"
       checkout "ns-rse/2-square-root"
       commit id: "4-8ec389a"
       checkout "ns-rse/1-zero-division"
       commit id: "5-2315fa0"
       checkout "ns-rse/2-square-root"
       commit id: "6-93e787c"
       checkout main
       merge "ns-rse/1-zero-division" id: "7-bc43901" tag: "v0.1.1"
       commit id: "HEAD"
       checkout "main"

%%{init: {'theme': 'base', 'gitGraph': {'rotateCommitLabel': true}
         }
}%%
    gitGraph
       accTitle: Merging Diverged Branches
       accDescr {After - main, which has already had the work in ns-rse/1-zero-division merged into it, is
       merged into ns-rse/2-square-root. Development is completed on ns-rse/2-square-root and the feature merged
       into main.}
       commit id: "0-472f101"
       commit id: "1-51816d6"
       commit id: "2-6769ff2 (base)"
       branch "ns-rse/1-zero-division"
       branch "ns-rse/2-square-root"
       checkout "ns-rse/1-zero-division"
       commit id: "3-8c52dce"
       checkout "ns-rse/2-square-root"
       commit id: "4-8ec389a"
       checkout "ns-rse/1-zero-division"
       commit id: "5-2315fa0"
       checkout "ns-rse/2-square-root"
       commit id: "6-93e787c"
       checkout main
       merge "ns-rse/1-zero-division" id: "7-bc43901" tag: "v0.1.1"
       commit id: "HEAD"
       checkout "ns-rse/2-square-root"
       merge "main" id: "8-a80cef8" tag: "Merge main"
       commit id: "9-cb839a0"
       commit id: "10-1ae54c3"
       checkout "main"
       merge "ns-rse/2-square-root" id: "11-a8c9932" tag: "v0.1.2"

%%{init: {'theme': 'base', 'gitGraph': {'rotateCommitLabel': true}
         }
}%%
    gitGraph
       accTitle: Rebase
       accDescr {Rebase.}
       commit id: "0-472f101"
       commit id: "1-51816d6"
       commit id: "2-6769ff2 (base)"
       branch "ns-rse/1-zero-division"
       checkout "ns-rse/1-zero-division"
       commit id: "3-8c52dce"
       checkout "ns-rse/1-zero-division"
       commit id: "5-2315fa0"
       checkout main
       merge "ns-rse/1-zero-division" id: "7-bc43901" tag: "v0.1.1"
       commit tag: "Rebase"
       branch "ns-rse/2-square-root"
       checkout "ns-rse/2-square-root"
       commit id: "4-8ec389a"
       checkout "ns-rse/2-square-root"
       commit id: "6-93e787c"
       commit id: "7-cb839a0"
       commit id: "8-1ae54c3"
       checkout "main"
       merge "ns-rse/2-square-root" id: "9-ba93020" tag: "v0.1.2"

Solution : git merge

The first thing to do is make sure main is up-to-date and has the changes that have been merged from the zero-division branch locally.

BASH

cd ~/work/git/hub/ns-rse/python-maths
git switch main
git pull

Then you can switch branches to the square-root branch and merge the main branch in.

BASH

git switch ns-rse/square-root
git merge main

You should have received a message about conflicts in the tests/test_arithmetic.py file.

BASH

git merge main
Auto-merging pythonmaths/arithmetic.py
Auto-merging tests/test_arithmetic.py
CONFLICT (content): Merge conflict in tests/test_arithmetic.py
Recorded preimage for 'tests/test_arithmetic.py'
Automatic merge failed; fix conflicts and then commit the result.

Solution : git rebase

The first thing to do is make sure main is up-to-date and has the changes that have been merged from the zero-division branch locally.

BASH

cd ~/work/git/hub/ns-rse/python-maths
git switch main
git pull

Then you can switch branches to the square-root branch and merge and rebase onto main.

BASH

git switch ns-rse/square-root
git rebase main

You should have received a message about conflicts in the tests/test_arithmetic.py file.

BASH

git rebase main
Auto-merging pythonmaths/arithmetic.py
Auto-merging tests/test_arithmetic.py
CONFLICT (content): Merge conflict in tests/test_arithmetic.py
error: could not apply bb4294a... feature: adds square root function
hint: Resolve all conflicts manually, mark them as resolved with
hint: "git add/rm <conflicted_files>", then run "git rebase --continue".
hint: You can instead skip this commit: run "git rebase --skip".
hint: To abort and get back to the state before "git rebase", run "git rebase --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Recorded preimage for 'tests/test_arithmetic.py'
Could not apply bb4294a... feature: adds square root function

Oh no I’ve got a `merge conflict`

Both the git merge and git rebase strategies in the examples we went through worked because none of the changes that were made touched the same files. In the Challenge though there was a conflict because both commits had added code to the end of tests/test_arithmetic.py and Git didn’t know which should be kept. This situation is known as “conflict” and resolving it requires manual intervention.

If you have undertaken the Git & GitHub Through GitKraken - From Zero to Hero! course you will have encountered merge conflicts when working through the “Python Calculator” exercise and have some idea of how to resolve them. We will however now go through resolving the issue when updating diverged branches.

Callout

`conflictStyle = diff3`

There is a useful tweak we can make to our configuration before working through resolving merge conflicts that makes it a little easier to see/understand what changes have been made. If we set the merge.conflictStyle = diff3 then we are shown the parent commit/state of one of the branches as well as the differences between the two.

Enable this now…

BASH

git config --global merge.conflictStyle = diff3

1. Create a new repository

BASH

cd ~/work/git/hub/ns-rse
mkdir git-rebase-conflict
cd git-rebase-conflict
git init --initial-branch=main
git commit --allow-empty -m "Initial commit"

2. Create `branch1` and add a `README.md`

Again we add a README.md but this time we make two commits to it, adding an extra line.

BASH

git switch -c branch1
echo -e "# Just a test\n\n" > README.md
git add README.md
git commit -m "docs: Adding README.md"
echo -e "Lets add another line in a separate commit" >> README.md
git add README.md
git commit -m "docs: Ooops, missed a line from the README.md"
git lol
* 59d399c - (HEAD -> branch1) docs: Ooops, missed a line from the README.md (2026-02-24 12:13:18 +0000) <Neil Shephard>
* 4901898 - docs: Adding README.md (2026-02-24 12:13:18 +0000) <Neil Shephard>
* 5750ad9 - (main) Initial commit (2026-02-24 12:12:55 +0000) <Neil Shephard>
(END)

3. Switch back to `main`

Again README.md doesn’t exist on this branch yet.

BASH

git switch main
cat README.md

4. Create `branch2` and add a `README.md`

We now set ourselves up for a conflict by creating a README.md on branch2, knowing full well that such a file already exists on branch1. We put different text into it.

BASH

git switch -c branch2
echo -e "# Just a test\n\nBut we're creating a merge conflict\n" > README.md
git add README.md
git commit -m "This repo needs a README.md"
cat README.md

5. Merge `branch1` into `main`

Switch to main and merge branch1. As we are done with this branch we can delete it now. The README.md has the text from branch1.

BASH

git switch main
git merge branch1
git branch -d branch1
cat README.md
# Just a test


Lets add another line in a separate commit

6. Switch to `branch2` and add another line to `README.md`

Switch back to branch2 and add another line to README.md, stage and commit it. The history now shows that we have two commits on this branch after the “Initial commit”.

BASH

# Switch to branch2 add more to `README.md` and rebase
git switch branch2
echo -e "Lets add another commit to make things messier" >> README.md
git add README.md
git commit -m "Bulking out README.md with more information"
git lol

* 22c7da7 - (HEAD -> branch2) Bulking out README.md with more information (2026-02-24 12:16:09 +0000) <Neil Shephard>
* bb1b362 - This repo needs a README.md (2026-02-24 12:14:39 +0000) <Neil Shephard>
* 5750ad9 - Initial commit (2026-02-24 12:12:55 +0000) <Neil Shephard>

6. Rebase `branch2` onto `main`

We now want to update branch2 by rebasing onto main so that we have the new changes from main (i.e. those merged from branch1). In this instance though we know both branch1 and branch2 have modified the file README.md and so we expect to get a conflict and sure enough we do.

BASH

git rebase main

Auto-merging README.md
CONFLICT (add/add): Merge conflict in README.md
error: could not apply bb1b362... This repo needs a README.md
hint: Resolve all conflicts manually, mark them as resolved with
hint: "git add/rm <conflicted_files>", then run "git rebase --continue".
hint: You can instead skip this commit: run "git rebase --skip".
hint: To abort and get back to the state before "git rebase", run "git rebase --abort".
Recorded preimage for 'README.md'
Could not apply fcfe2db... This repo needs a README.md

Oh dear we have, as expected, encountered the dreaded “merge conflict” as both branch1 and branch2 made changes to README.md in the same place. Lets take a look at what the file now looks like.

BASH

cat README.md
<<<<<<< HEAD
# Just a test


Lets add another line in a separate commit
||||||| parent of bb1b362 (This repo needs a README.md)
=======
# Just a test

But we're creating a merge conflict

>>>>>>> bb1b362 (This repo needs a README.md)

Here HEAD refers to the current branch that we have checked out (main) which includes the changes we made on branch1 and merged into main. The text that this refers to is delimited by <<<<<<< and |||||||.

The parent of bb1b362 on is present because we set merge.conflictStyle = diff3 and so we are shown the state of the file at this point before commit bb1b362 was made between ||||||| and =======, in this case it is empty because there was no README.md file. The last section between ======= and >>>>>>> bb1b362 (This repo needs a README.md) shows what was added by the commit bb1b362.

We are given some useful information as to what we could do and there are three options.

Resolve all conflicts manually, mark them as resolved with "git add/rm <conflicted files>", then run "git rebase --continue".
You can instead skip this commit: run "git rebase --skip".
To abort and get back to the state before "git rebase", run "git rebase --abort".

These are really useful messages telling us how we can proceed. In this instance we want to take option 1, so we should open the README.md and edit it to leave it in the state we want the file to be in.

7. Resolve the conflict

You can use the nano editor to open the file with nano README.md. Edit it to look like this:

BASH

# Just a test

Lets add another line in a separate commit

But we're creating a merge conflict

Callout

Nano

In nano You can use Ctrl+k to cut a whole line at once (Ctrl+u inserts the line that was last removed). Save the file and return to the command prompt (in nano this is Ctrl+O then Ctrl+X).

A useful bookmark to help whilst developing the muscle memory for the commands is the nano shortcuts cheatsheet.

It is possible that your system may use a different editor than nano by default, e.g. vim. It does not matter which text editor you use to edit and save the files.

8. Add the conflicted file and continue with rebase

You can now continue with the advice and add the conflicted files back to Git and continue with the rebase.

BASH

git add README.md
git rebase --continue

Recorded resolution for 'README.md'.
[detached HEAD d041adb] This repo needs a README.md
 1 file changed, 4 insertions(+)
Auto-merging README.md
CONFLICT (content): Merge conflict in README.md
error: could not apply 22c7da7... Bulking out README.md with more information
hint: Resolve all conflicts manually, mark them as resolved with
hint: "git add/rm <conflicted_files>", then run "git rebase --continue".
hint: You can instead skip this commit: run "git rebase --skip".
hint: To abort and get back to the state before "git rebase", run "git rebase --abort".
error: could not parse conflict hunks in 'README.md'
Could not apply 22c7da7... Bulking out README.md with more information

Hang on, we just resolved the merge conflict why are we being told there is another? Well the first conflict was with commit bb1b362 and has been resolved and we are told as much in the line Recorded resolution for 'README.md', however there is now a conflict between that and commit 22c7da7. We get the same advice so lets take a look at the state of README.md

BASH

# Just a test

Lets add another line in a separate commit

<<<<<<< HEAD
But we're creating a merge conflict
||||||| parent of 22c7da7 (Bulking out README.md with more information)
=======
Lets add another commit to make things messier
>>>>>>> 22c7da7 (Bulking out README.md with more information)

Here we can see it’s the second line that we added to README.md under branch2 that read Lets add another commit to make things messier that is causing the problem. It’s not in the main branch on which we are rebasing so Git doesn’t know whether it should be and we have to manually resolve this. Edit the file so that it looks like the following.

BASH

# Just a test

Lets add another line in a separate commit

But we're creating a merge conflict

Lets add another commit to make things messier

9. Add the conflicted file and continue with the second stage of the rebase

Then add the conflicted file and continue with the rebase.

BASH

git add README.md
git rebase --continue
[detached HEAD 0ccfe91] Bulking out README.md with more information
 1 file changed, 1 insertion(+), 1 deletion(-)
Successfully rebased and updated refs/heads/branch2.

We are told that the rebase has been successful and branch2 now contains all commits from main (which includes those merged from branch1). If we look at the contents of README.md it contains all of the lines we added to both branches as that is how we chose to resolve the conflicts manually.

BASH

cat README.md
# Just a test


Lets add another line in a separate commit

But we're creating a merge conflict

Lets add another commit to make things messier

The history/graph is linear now and shows that branch2 is two commits ahead of main.

BASH

git lol

* 0a7f5db - (HEAD -> branch2) Bulking out README.md with more information (2026-02-24 12:16:09 +0000) <Neil Shephard>
* ae93af0 - This repo needs a README.md (2026-02-24 12:14:39 +0000) <Neil Shephard>
* 59d399c - (main) docs: Ooops, missed a line from the README.md (2026-02-24 12:13:18 +0000) <Neil Shephard>
* 4901898 - docs: Adding README.md (2026-02-24 12:13:18 +0000) <Neil Shephard>
* 5750ad9 - Initial commit (2026-02-24 12:12:55 +0000) <Neil Shephard>

Callout

You may be wondering why when performing git rebase it mentions git merge. This is because a rebase will sequentially merge all commits from the branch you are rebasing onto, in this case main, into the HEAD of your current checked out branch (branch2).

Repeating yourself

You only had to resolve two merge conflicts here, if the history you are merging has a lot of commits you may end up solving the same merge conflict repeatedly and wonder why you keep on getting asked to resolve the same conflict. There is a way to avoid this though.

Callout

Avoid divergence if possible

Bringing a diverged branch up-to-date can get very messy and confusing if there is a large amount of divergence. The best strategy to avoid this complication is two fold.

Break work down into small chunks and regularly merge them into main.
If this can not be avoided or lots of others are making changes you should git merge or git rebase your feature branch onto main frequently.

Even if you keep your work and branches small you may still encounter this situation and find that you are repeatedly resolving the same conflict as you want the finer grained control over git rebase and one option is to git rebase --abort and use git merge instead as you only have to resolve the conflicts once, although there may be a lot of them. One disadvantage of this is it makes it look like the commits stem from you and so many people prefer the rebase strategy.

Help is at hand though if you find you are repeatedly being asked to resolve the same conflict as you progress through a rebase in the form of rerere which stands for “reuse recorded resolution” and causes Git to remember how it has resolved merge conflicts at a given point and the next time it is encountered it will use the solution from the first instance.

You can enable this in your global configuration, which is covered in greater detail in the next episode, with the following.

BASH

git config --global rerere.enabled true

If you only wish to use this strategy on some repositories you can apply it to your local configuration from within the working directory.

BASH

git config --local rerere.enabled true

You can of course enable globally and disable locally as local configuration variables take precedence over global.

Callout

Squash commits before rebasing/merging

If you have lots of small commits you can perform an interactive rebase (git rebase -i HEAD^^^^^^^^^) to squash these into a single commit prior to initiating the rebase or merge.

Challenge

Challenge 2: Diverging Branches

You didn’t complete the merge/rebase in the previous challenge because of the merge conflict. In your pairs do so now.

If we look at the conflict in tests/test_arithmetic.py we can see at the bottom the sections that are conflicting. They are de-marked by <<<<<<<, |||||||, ======= and >>>>>>> and the HEAD and <commit-hash> show which branches they originate from.

The exact solution will depend on the strategy you have chosen (merge or rebase) to bring the branch up-to-date.

Solution 1 : git merge

BASH

cat tests/test/arithmetic.py
<<<<<<< HEAD


@pytest.mark.parametrize(
    ("x", "target"),
    [
        pytest.param(4, 2, id="square root of 4"),
        pytest.param(9, 3.0, id="square root of 9"),
        pytest.param(25, 5.0, id="square root of 25"),
        pytest.param(2, 1.4142135623730951, id="square root of 2"),
    ],
)
def test_square_root(x: int | float, target: int | float) -> None:
    """Test the square_root() function."""
    pytest.approx(arithmetic.square_root(x), target)
||||||| 80b95c0
=======


def test_divide_zero_division_exception() -> None:
    """Test that a ZeroDivisionError is raised by the divide() function."""
    with pytest.raises(ZeroDivisionError):
        arithmetic.divide(2, 0)
>>>>>>> main

We know that we want both of these changes so we can edit the file and remove the delimiters to leave it looking like the following.

Then you can switch branches to the square-root branch and merge the main branch in.

BASH



@pytest.mark.parametrize(
    ("x", "target"),
    [
        pytest.param(4, 2, id="square root of 4"),
        pytest.param(9, 3.0, id="square root of 9"),
        pytest.param(25, 5.0, id="square root of 25"),
        pytest.param(2, 1.4142135623730951, id="square root of 2"),
    ],
)
def test_square_root(x: int | float, target: int | float) -> None:
    """Test the square_root() function."""
    pytest.approx(arithmetic.square_root(x), target)


def test_divide_zero_division_exception() -> None:
    """Test that a ZeroDivisionError is raised by the divide() function."""
    with pytest.raises(ZeroDivisionError):
        arithmetic.divide(2, 0)

If you check the status you see that you are in the middle of a merge and that tests/test_arithmetic.py has been modified by both.

BASH

git status
On branch ns-rse/2-square-root
Your branch is up to date with 'origin/ns-rse/2-square-root'.

You have unmerged paths.
  (fix conflicts and run "git commit")
  (use "git merge --abort" to abort the merge)

Changes to be committed:
    modified:   pythonmaths/arithmetic.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
    both modified:   tests/test_arithmetic.py

You now need to stage your changes and commit them.

BASH

git add -u
git commit
git push

You can now create a pull request, assign it for review and merge it.

Solution 2 : git rebase

BASH

cat tests/test/arithmetic.py
<<<<<<< HEAD


@pytest.mark.parametrize(
    ("x", "target"),
    [
        pytest.param(4, 2, id="square root of 4"),
        pytest.param(9, 3.0, id="square root of 9"),
        pytest.param(25, 5.0, id="square root of 25"),
        pytest.param(2, 1.4142135623730951, id="square root of 2"),
    ],
)
def test_square_root(x: int | float, target: int | float) -> None:
    """Test the square_root() function."""
    pytest.approx(arithmetic.square_root(x), target)
||||||| 80b95c0
=======


def test_divide_zero_division_exception() -> None:
    """Test that a ZeroDivisionError is raised by the divide() function."""
    with pytest.raises(ZeroDivisionError):
        arithmetic.divide(2, 0)
>>>>>>> main

We know that we want both of these changes so we can edit the file and remove the delimiters to leave it looking like the following.

Then you can switch branches to the square-root branch and merge the main branch in.

BASH



@pytest.mark.parametrize(
    ("x", "target"),
    [
        pytest.param(4, 2, id="square root of 4"),
        pytest.param(9, 3.0, id="square root of 9"),
        pytest.param(25, 5.0, id="square root of 25"),
        pytest.param(2, 1.4142135623730951, id="square root of 2"),
    ],
)
def test_square_root(x: int | float, target: int | float) -> None:
    """Test the square_root() function."""
    pytest.approx(arithmetic.square_root(x), target)


def test_divide_zero_division_exception() -> None:
    """Test that a ZeroDivisionError is raised by the divide() function."""
    with pytest.raises(ZeroDivisionError):
        arithmetic.divide(2, 0)

If you check the status you see that you are in the middle of a merge and that tests/test_arithmetic.py has been modified by both.

BASH

git status
On branch ns-rse/2-square-root
Your branch is up to date with 'origin/ns-rse/2-square-root'.

You have unmerged paths.
  (fix conflicts and run "git commit")
  (use "git merge --abort" to abort the merge)

Changes to be committed:
    modified:   pythonmaths/arithmetic.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
    both modified:   tests/test_arithmetic.py

You now need to stage your changes and commit them.

BASH

git add -u
git rebase --continue
git push

You can now create a pull request, assign it for review and merge it.

Callout

Merge or Rebase

Arguments rage online between experienced users as to whether you should git merge or git rebase. It can often be a matter of preference and you should agree within your team which strategy to use and stick with it.

However it is worth noting that if you git merge your changes from the main branch into your feature branch when you come to merge your feature branch into main via a Pull Request then the git diff will show all changes for commits that have been merged into main since your feature branch was made and not just the changes you have made in your feature branch (i.e. the commits that have already been merged into main also appear in your pull request). This can make reviewing pull requests considerably harder and is a good case for using git rebase to keep your feature branches up-to-date when you know they have diverged.

On the flip side it can be very difficult to recover from a git rebase that has gone wrong and there is scope that you might lose work making git merge a safer option.

Key Points

Branches can become outdated as work progresses
Branches can be brought up-to-date with either git merge or git rebase.

Diverging Branches

Overview

Questions

Objectives

Diverging Branches

Merging

BASH

1. Make a new repository

BASH

2. Create branch1, add a README.md and commit it

BASH

3. Switch back to main

BASH

4. Create branch2, add a LICENSE and commit it

BASH

5. Merge branch1 into main

BASH

6. Merge main, which now contains README.md, into branch2

BASH

7. Merge branch2 into main

BASH

8. Delete branch1 and branch2

BASH

Rebasing

1. Make a new repository

BASH

2. Create branch1, add a README.md and commit it

BASH

3. Switch back to main

BASH

4. Create branch2, add a LICENSE and commit it

BASH

5. Merge branch1 into main (equivalent to making a Pull Request)

BASH

6. Rebase branch2 onto main so it includes the README.md and the point of divergence is updated

BASH

7. Merge branch2 into main

BASH

8. Delete branch1 and branch2

BASH

Challenge 1: Diverging Branches

Solution : git merge

BASH

BASH

BASH

Solution : git rebase

BASH

BASH

BASH

Oh no I’ve got a merge conflict

conflictStyle = diff3

BASH

1. Create a new repository

BASH

2. Create branch1 and add a README.md

BASH

3. Switch back to main

BASH

4. Create branch2 and add a README.md

BASH

5. Merge branch1 into main

BASH

6. Switch to branch2 and add another line to README.md

BASH

6. Rebase branch2 onto main

BASH

BASH

7. Resolve the conflict

BASH

Nano

8. Add the conflicted file and continue with rebase

BASH

BASH

BASH

9. Add the conflicted file and continue with the second stage of the rebase

BASH

BASH

BASH

Repeating yourself

Avoid divergence if possible

2. Create `branch1`, add a `README.md` and commit it

3. Switch back to `main`

4. Create `branch2`, add a `LICENSE` and commit it

5. Merge `branch1` into `main`

6. Merge `main`, which now contains `README.md`, into `branch2`

7. Merge `branch2` into `main`

8. Delete `branch1` and `branch2`

2. Create `branch1`, add a `README.md` and commit it

3. Switch back to `main`

4. Create `branch2`, add a `LICENSE` and commit it

5. Merge `branch1` into `main` (equivalent to making a Pull Request)

6. Rebase `branch2` onto `main` so it includes the `README.md` and the point of divergence is updated

7. Merge `branch2` into `main`

8. Delete `branch1` and `branch2`

Oh no I’ve got a `merge conflict`

`conflictStyle = diff3`

2. Create `branch1` and add a `README.md`

3. Switch back to `main`

4. Create `branch2` and add a `README.md`

5. Merge `branch1` into `main`

6. Switch to `branch2` and add another line to `README.md`

6. Rebase `branch2` onto `main`