Stop 03 · Git & GitHubTopics · 5/11

Merge

In short

Your feature works on its branch. Now it has to join main so it can ship. Merge is how two lines of work become one.

`git merge` combines the history of one branch into another, creating a merge commit (or fast-forwarding) to bring the changes together.

The mascot in an apron pours two different curries into one steel thali.

Think of it like this

Two cooks, one thali

One cook makes dal, another makes sabzi, in separate kitchens. At serving time, both go into the same thali. Nothing is thrown away. git merge brings the work of two branches together onto one plate.

Watch it happen

Two kinds of merge

Fast-forward

main had no new commits
main pointer simply slides ahead
No extra merge commit created

Three-way merge

Both branches got new commits
Git combines them using the common ancestor
Creates a merge commit with two parents

Git picks automatically. Use --no-ff if your team wants a merge commit every time for clarity.

The big ideas

What you need to know

Merge into where you are

git merge feature/login brings that branch into your current branch. So switch to main first.

Merge commits have two parents

That's how Git remembers that two lines of work joined at this point.

Conflicts are normal

If both sides changed the same lines, Git stops and asks you to pick. It's not an error, just a question.

Pull main first

Before merging locally, git pull on main so you merge into the latest version, not an old copy.

See it in code

Walk through the code

bash

1git switch main2git pull                       # get the latest main3 4git merge feature/login        # bring login work in5# Fast-forward or "Merge made by the 'ort' strategy."6 7git log --oneline --graph -6   # see the join8git push                       # share the merged main9git branch -d feature/login

1/3Stand on main and make sure it's up to date before merging anything into it.

ort is Git's default merge strategy today. You don't need to choose it; it's just what the message says.

Save yourself the pain

Common mistakes

Oops

Running git merge main while on main, and wondering why nothing happens.

Do this instead

Switch to the branch that should receive the work, then merge the other branch name into it.

Oops

Panicking at a conflict and deleting the whole folder.

Do this instead

Run git merge --abort to go back to before the merge, then try again calmly.

Your mission

Both kinds of merge

~20 min

Quick check

main has no new commits since you branched. You merge your branch into main. What happens?

Go deeper

1Merge a feature branch into `main` and inspect the resulting commit graph.
2Learn the difference between a fast-forward merge and a 3-way merge.
3Deliberately create a merge conflict in a sandbox repo to practice resolving it.