Branches

Goal#

Make branches, switch between them, see history as a graph, and merge.

A branch is a sticky note#

main is a label on one commit. When you commit on main, the label moves to the new commit. A new branch is a new label; HEAD says which label you are carrying.

git branch                       # list branches; * marks yours
git switch -c nap-time           # create a branch here and move onto it
git switch main                  # move back
git log --oneline --graph --all  # every branch, drawn as a graph

Make git log --oneline --graph --all a habit. It turns branches from a mystery into a picture.

Two kinds of merge#

git merge treats brings the commits of treats into the branch you are on.

• Fast-forward. If your branch has not moved since treats started, git just slides your label forward. No new commit.
• Three-way merge. If both branches have new commits, git makes a merge commit with two parents, joining the lines in the graph.

Quest 04#

quest start 4

The treats branch is ready. Then HEAD wants to plan nap time on a branch of her own:

1. Merge treats into main.
2. Make a branch called nap-time, and commit something on it.
3. Merge nap-time into main, and finish on main.

Draw the graph after every step. Then quest check.

Check it works#

• git log --oneline --graph --all shows both branches inside main.
• quest check passes.

Exercise#

Make a commit on main and another on a new branch, so both have moved, then merge. Look at the graph: there is your three-way merge commit, with two parents. git show --format=%P -s HEAD prints them.

More to try

• Delete a merged branch with git branch -d nap-time. The commits stay; only the label goes.
• Try git merge --no-ff on a fast-forward. When would a team want that?