The Tree of Possibilities

Introduction

"Apprentice, until now you have worked on a single timeline - a unique, linear chronicle where each event follows the previous one. But great Archivists know something novices do not: history does not have just one possible path. Look at this tree. Each branch represents a parallel timeline - a possible future for the kingdom. You can explore these branches, record events on them, and decide later which one will become the official chronicle. This is the power of Git branches."

What is a branch?

Until now, all your commits have been chained on a single branch: main (formerly "master"). It is the official chronicle - the main timeline of the project.

Why use branches?

• Experiment without risk: you test an idea on a branch. If it works, you keep it. If not, you delete it.
• Work in parallel: while a colleague works on one feature, you work on another, each on your own branch.
• Keep main clean: the main branch only contains validated and tested code.

View existing branches

To list all branches in your repository:

git branch

The current branch is marked with an asterisk * and appears in green:

* main

For now, you only have one branch. That is about to change.

Create a new branch

To create a branch without switching to it:

git branch <name>

Example:

git branch expedition-nord

This creates a branch expedition-nord that points to the same commit as your current branch. But you are still on main - you have not changed timelines.

Verify:

git branch

  expedition-nord
* main

The asterisk is still on main.

Switch to a branch

The modern command: git switch

git switch expedition-nord

This is the recommended method since Git 2.23. Simple, clear, unambiguous.

The old method: git checkout

git checkout expedition-nord

You will see git checkout in many tutorials and existing projects. It works, but git switch is more explicit because git checkout also does other things (like restoring files, for example).

Create and switch in one command

You can combine creation and switching:

git switch -c new-branch

Or with the old syntax:

git checkout -b new-branch

HEAD - The position marker

HEAD is a special pointer that indicates where you currently are in the history. More precisely, HEAD points to the current branch, which itself points to a commit.

HEAD -> main -> commit C3
         expedition-nord -> commit C3

When you run git switch expedition-nord:

         main -> commit C3
HEAD -> expedition-nord -> commit C3

And when you make a new commit on expedition-nord:

         main -> commit C3
HEAD -> expedition-nord -> commit C4

Delete a branch

Safe deletion

git branch -d branch-name

The -d option (lowercase) deletes the branch only if it has been merged. This is a safety measure: Git refuses to delete a branch that contains unintegrated work.

Forced deletion

git branch -D branch-name

Practical exercise - The Parallel Chronicles

Step 1 - Create the repository

Create a new folder and initialize a Git repository:

mkdir chroniques-paralleles
cd chroniques-paralleles
git init -b main

Step 2 - First commit on main

Create a base file and make your first commit:

echo "# Chronicles of the Kingdom" > chroniques.md
git add chroniques.md
git commit -m "Create the kingdom chronicles registry"

Step 3 - Create the expedition-nord branch

git branch expedition-nord

Step 4 - Switch to expedition-nord

git switch expedition-nord

Verify that you are on the right branch:

git branch

You should see the asterisk on expedition-nord.

Step 5 - Commit on expedition-nord

Create a file and commit it:

echo "Day 1: The expedition leaves the city towards the Frost Mountains." > nord.md
git add nord.md
git commit -m "Add the northern expedition journal"

Step 6 - Return to main

git switch main

Step 7 - Create and switch to expedition-sud

This time, combine both in a single command:

git switch -c expedition-sud

Step 8 - Commit on expedition-sud

echo "Day 1: The expedition ventures into the Emerald Forest." > sud.md
git add sud.md
git commit -m "Add the southern expedition journal"

Step 9 - List all branches

git branch

You should see three branches: expedition-nord, expedition-sud (with the asterisk), and main.

Step 10 - Verify

Run the verification script to validate your quest:

Bash (Linux / macOS / Git Bash on Windows):

bash verifier.sh

PowerShell (Windows):

.\verifier.ps1

The script checks:

1. You are in a Git repository
2. The expedition-nord branch exists
3. The expedition-sud branch exists
4. The expedition-nord branch contains at least one unique commit
5. The expedition-sud branch contains at least one unique commit
6. There are at least 3 branches in total
7. You are back on the main branch

Command summary