Stop 05 · Git & GitHubTopics · 5/11

Merge

In short

Your feature works on its branch. Now it needs to go back into main. Merging joins the two lines of work into one.

`git merge` combines the history of one branch into another, creating a merge commit (or fast-forwarding) to bring the changes together. Merge preserves the relationship between histories and is particularly useful when multiple lines of development need to be brought together explicitly.

The jaadu mascot in an apron pours dal and sabzi from two pots onto one steel thali.

Think of it like this

Two cooks, one thali

In a hostel mess, one cook makes dal while another makes sabzi. At lunchtime both go onto the same thali. Merging is that moment. Usually it just works. Trouble only comes if both cooks changed the same dish.

Watch it happen

Merging a finished feature

Feature branch

Local main

GitHub

all work committed

1/5Everything on feature/dark-mode is committed. Nothing is left half-done.

The big ideas

What you need to know

Fast-forward merge

If main hasn't moved since you branched, Git simply slides main forward to your latest commit.

Merge commit

If both branches have new commits, Git makes a special commit that joins them, with two parents.

Merge into where you stand

Switch to the branch that should receive the changes (usually main), then merge the other one in.

Same lines means conflict

If both sides edited the same lines, Git stops and asks you to pick. That's a merge conflict.

See it in code

Walk through the code

bash

1git switch main2git pull                        # get the latest main3git merge feature/dark-mode     # bring the feature in4 5git log --oneline --graph -10   # see how the lines joined6git push7 8git branch -d feature/dark-mode

1/4Stand on main and update it, so you merge into what your team has right now.

The --graph flag draws the branches as lines in your terminal, so you can actually see where they split and joined.

Save yourself the pain

Common mistakes

Oops

Running git merge main while standing on main and expecting the feature to arrive.

Do this instead

Merge brings the named branch into your current one. Stand on main, then merge the feature branch.

Oops

Merging into an old copy of main.

Do this instead

Run git pull on main first, so you merge into what your team has right now.

Your mission

See both kinds of merge

~20 min

Quick check

You merge a branch into main and Git says 'Fast-forward'. What happened?

Go deeper

1Merge a feature branch into `main` and inspect the resulting commit graph. Validate your understanding by applying it in a small practical example.
2Learn the difference between a fast-forward merge and a 3-way merge. Focus on understanding the underlying reason it works, not only memorizing the definition.
3Deliberately create a merge conflict in a sandbox repo to practice resolving it.