Session 5 · Branches

⏱ about 60 minutes · 🧰 you need: Session 4 done

The big idea

A branch is a separate line of work. It lets you try a new feature, fix a bug or run an experiment without touching the stable version of your project. When the work is good, you bring it back (a merge, next session). If it is bad, you delete the branch and nothing is lost.

Everyday example: you are writing a book. Instead of scribbling directly in the master manuscript, you photocopy it, write a risky new chapter on the copy, and only if the editor likes it do you paste it into the master. The master is main; the photocopy is a branch.

In real life you never pause the main project while someone builds a feature. Branches make it possible for ten people to work on ten features at once.

1. A branch is just a sticky label

This is the one fact that makes branches click:

A branch is only a movable label that points at one commit. Nothing is copied. Creating a branch takes a few milliseconds.

main and feature are just labels on commits; feature has two commits that main does not have yet.

• main is the label on the latest commit of the main line.

• feature is another label; it has two commits main does not have.

• When you commit while on a branch, the label moves forward to the new commit.

2. HEAD: “you are here”

Git needs to know which branch you are on. A special pointer called HEAD says so. HEAD points to a branch; the branch points to a commit.

HEAD points at a branch, and the branch points at a commit; git switch moves HEAD to another branch.

Your next commit is added to whatever HEAD’s branch is, and that branch’s label moves forward.

3. Try it: create and switch

Start from a fresh repo:

cd ~/git-lab
mkdir branch-lab && cd branch-lab
git init
echo "<h1>My Shop</h1>" > index.html
git add . && git commit -m "Add shop homepage"
echo "<p>Contact: shop@example.com</p>" >> index.html
git commit -am "Add contact line"

See your branches:

git branch

* main

The * marks the branch you are on. Create a new branch and move onto it:

git switch -c cart-page

Switched to a new branch 'cart-page'

-c means create. It is the shortcut for two steps: git branch cart-page (make the label) then git switch cart-page (move HEAD to it).

git branch

* cart-page
  main

4. Work on the branch

echo "<h2>Your cart</h2>" > cart.html
git add cart.html
git commit -m "Add cart page"
echo "<p>0 items</p>" >> cart.html
git commit -am "Show item count in cart"
git log --oneline --graph --all

* 5c5c5c5 (HEAD -> cart-page) Show item count in cart
* 4b4b4b4 Add cart page
* 2a2a2a2 (main) Add contact line
* 1a1a1a1 Add shop homepage

cart-page is two commits ahead of main. Now go back to main:

git switch main
ls

index.html

cart.html is gone from your folder! It is not lost: it lives on the cart-page branch. When you switch, Git rewrites your working folder to match that branch’s snapshot.

git switch cart-page
ls

cart.html  index.html

It is back. 🎩

Important

Before switching branches, commit (or stash) your work. If you have uncommitted changes that conflict with the other branch, Git refuses to switch and tells you why. (Session 9 shows git stash, a safe shelf for half-done work.)

5. Everyday branch commands

Command	What it does
git branch	list local branches (* = current)
git branch -a	also list branches on the remote
git branch -v	list branches with their latest commit
git switch name	move to an existing branch
git switch -c name	create a branch and move to it
git switch -c name <start-point>	create it starting from a specific commit or branch
git branch -m old new	move / rename a branch
git branch -d name	delete a branch that is already merged (safe)
git branch -D name	force delete, even unmerged (careful)
git log --oneline --graph --all	draw all branches

Note

Older tutorials use git checkout branch and git checkout -b branch. They still work. git switch (for branches) and git restore (for files) are the newer, clearer commands that replaced the two jobs of checkout.

6. A branch splits when both lines get new commits

git switch main
echo "<footer>shop@example.com</footer>" >> index.html
git commit -am "Add footer to homepage"
git log --oneline --graph --all

* 7d7d7d7 (HEAD -> main) Add footer to homepage
| * 5c5c5c5 (cart-page) Show item count in cart
| * 4b4b4b4 Add cart page
|/
* 2a2a2a2 Add contact line
* 1a1a1a1 Add shop homepage

The history has diverged: both main and cart-page have commits the other lacks. Joining them is the job of merging, the next session.

7. Naming branches

Good branch names say what the work is. Common team conventions:

Pattern	Example
feature/<what>	feature/cart-page, feature/login
bugfix/<what>	bugfix/wrong-total
hotfix/<what>	hotfix/payment-crash
release/<version>	release/1.4.0
docs/<what>	docs/update-readme
with a ticket number	feature/SHOP-142-cart-page

Use lower case, no spaces (use -). Short, but specific.

Common mistakes

Mistake	Fix
“My file disappeared!” after switching	It lives on the other branch. git switch - goes back to where you were.
Committing on main by accident	Create a branch from here: git switch -c feature/x, then move main back (Session 12, wrong branch).
error: Your local changes would be overwritten by checkout	Commit first, or git stash (Session 9).
Deleting a branch with -D and losing unmerged work	Reflog can find the commit (Session 4). Prefer -d, which refuses to delete unmerged work.
Working for weeks on one huge branch	Merging gets painful. Keep branches short and merge often.

Hands-on exercises

Tryout 1 · Branch out. In branch-lab, create a branch feature/search from main, add a file search.html, and commit it. Then return to main and confirm search.html is not there.

Answer

git switch main
git switch -c feature/search
echo "<input type=search>" > search.html
git add search.html
git commit -m "Add search page"
git switch main
ls                      # no search.html

Tryout 2 · Draw. Run git log --oneline --graph --all. How many branches have commits that main lacks?

Answer

Two: cart-page (2 commits) and feature/search (1 commit). Both split off the line of main, so each shows as a side branch in the graph.

Tryout 3 · Rename and delete. Rename feature/search to feature/site-search, then try to delete it with the safe option. What does Git say, and why?

Answer

git branch -m feature/search feature/site-search
git branch -d feature/site-search

error: the branch 'feature/site-search' is not fully merged.

Git protects you: its commit is not on any other branch yet. Use -D only if you really want to discard it.

Recap

• ✅ A branch is a movable label on a commit. Creating one is instant and free.

• ✅ HEAD says which branch you are on; new commits move that branch’s label.

• ✅ git switch -c name creates and moves; git switch name moves; git branch lists.

• ✅ Switching branches changes the files in your folder to match that branch.

• ✅ Use clear names such as feature/... and bugfix/....

Next: Session 6 · Merging and Conflicts.