Git Branches, Merging and Conflicts

What it is

A Git branch is a separate line of development that lets you change code without touching the main line.

When the work is finished and tested, you merge the branch back. Sometimes Git cannot combine two changes by itself, and you resolve a merge conflict by hand.

Branching is cheap in Git, so teams create one for each feature, fix or experiment.

How it works

Branches are pointers to commits, and merging joins two histories together.

Working with branches

$ git branch
$ git branch add-vlan-check
$ git checkout add-vlan-check
$ git switch main
$ git checkout -b fix-typo

• git branch lists the branches and marks the current one.
• git branch NAME creates a branch.
• git checkout NAME and git switch NAME move to a branch.
• git checkout -b NAME creates a branch and switches to it in one step.

New commits go onto the branch you are on. The files in your folder change to match the branch you switch to.

Merging

To merge, switch to the branch that should receive the changes, then run git merge with the name of the other branch.

$ git switch main
$ git merge add-vlan-check

There are two common results.

After a successful merge you can delete the finished branch with git branch -d add-vlan-check.

Merge conflicts

A conflict happens when two branches change the same lines of the same file, or when one branch deletes a file that the other changed. Git cannot decide which version is right, so it stops and asks you.

Git marks the problem area in the file with three kinds of line:

• A line of seven less than signs starts your version, labelled HEAD.
• A line of seven equals signs separates the two versions.
• A line of seven greater than signs ends the other version, labelled with its branch name.

Auto-merging config.yaml
CONFLICT (content): Merge conflict in config.yaml
Automatic merge failed; fix conflicts and then commit the result.

Resolving a conflict

1. Run git status to see which files are in conflict.
2. Open each file and decide what the final text should be. Keep one side, or combine both.
3. Delete the marker lines, so only the final text remains.
4. Run git add on the fixed file.
5. Run git commit to complete the merge.

$ git status
$ git add config.yaml
$ git commit -m "Merge add-vlan-check and resolve config conflict"

If you want to give up, git merge --abort returns to the state before the merge.

Comparing branches

Before you merge, git diff main add-vlan-check shows what differs between the two branches. It uses the same unified diff form as other Git diffs.

Sharing a branch

A new branch exists only on your machine until you push it.

$ git push origin add-vlan-check

Many teams then open a pull request or merge request. A reviewer checks the changes before they are merged into the main branch.

Good habits

• Keep branches short lived, so the gap to main stays small.
• Pull the latest main into your branch often, to find conflicts early.
• Commit small, focused changes. Small changes conflict less.