Create a new branch, switch between branches, and watch two storylines split apart.
Excellent progress. You have built a strong foundation already. So far, every page has gone into one section of the scrapbook called main, the default section every new scrapbook starts with.
Most scrapbookers, and programmers, like to create extra sections so they can try out new ideas without messing up their main storyline. Git makes that easy. Those sections are called branches, and in nerd-speak making one is lightweight, which just means quick and simple.
A branch is basically a section marker labelling one scrapbook page, one commit. That is why the green main marker has always sat on top of the latest page you made.
Each page connects back to the one before it, forming a chain, and Git follows those links to read the full story. So you can think of a branch as its own storyline of connected pages that form a section in the book, while Git itself treats it as nothing more than a marker on the most recent page of that storyline.
git branch <new-branch-name>
This creates a new section marker pointing at your current page. Besides main, which scrapbookers usually reserve for finalized pages, it is common to make a dev section for work in progress.
Make the dev section:
git branch devSee that shiny new green marker called dev stacked on your latest page? That is the section marker you just created. The old main marker is still there too, because both markers point at the exact same page right now.
Branches are just markers that point at pages. Nothing more, nothing less. So for the moment main and dev mark the same page, and that is perfectly normal.
But remember: even though you made dev, you are still actively working on main. The HEAD clip is still on the main marker. If you kept committing now, the new pages would keep going into main.
To start adding pages to the dev section, you need to switch to it first:
git switch <branch-name>
Move onto the new section:
git switch devHuzzah. HEAD hopped from main to dev. Now you are ready to add a page in the dev section and see what happens.
You change the file friend.py that Your Friend added, so it says:
print("Hi best friend!")
Since you updated friend.py, that memento has changed. It appears on the table with its pencil badge, and the next two steps are the usual ones: stage it, commit it.
Onto the mat.
git add friend.pyCommit it:
git commit -m "Say hi to a best friend"Well would you look at that. Notice you did not have to mention dev when making the commit. Because you switched to dev earlier, every new page you commit automatically goes into that section.
As usual, the new page was added at the front. But this time only the dev marker and HEAD moved onto it. main is still sitting on the earlier page. What gives?
Since you switched to dev, it became the active section of your scrapbook, and main is no longer active. Three statements that all mean the same thing:
dev is the active branch.dev is currently checked out.dev.Whenever you make a new page, the active branch's marker moves forward to it. Other markers stay put, marking whatever page they were on. So now you have two sections that no longer match: dev is one page ahead of main, but all the earlier pages still belong to both. Trace the arrows back from each marker and they share the same history until... they don't.
So what would happen if you switched back to main and added a page there? Let's find out.
git switch mainHEAD jumps back onto the main marker, and your files change to match main's latest page: friend.py says Hi friend! again on your table. Your edit is safe on the dev page.
Now that main is checked out, you are ready to add a page here. You create a new memento called birthday.py with this code inside:
print("It's mah birfday!")
Brand new memento, so it shows up untracked. Stage it, then commit it.
To the staging area.
git add birthday.pyCommit the new page on main:
git commit -m "Add birthday.py"Unbe-LEAF-able. Look what happened to main. It split off from dev. But why?
Because you added different pages to each branch. On dev you changed the memento in friend.py. Then on main you added the brand new memento birthday.py. Trace back from both markers and you will find the same shared parent page. From there, they have diverged into separate storylines.
dev does not know about the latest main page, and main does not know about the latest dev page. Kind of sad if you think about it. But do not shed too many tears: this happens all the time in Git.
Picture it: you are working on a storyline about your birthday party while Your Friend builds one about their holiday trip. You keep your pages in a section called birthday-party, they keep theirs in holiday-trip. Eventually you both want to combine the storylines so the scrapbook has everybody's memories. In Git, combining storylines is called merging, and that is Level 8.
You want to keep working in the dev section. Which command takes you there?
(We will stay on main for now, because that is where the merge in Level 8 needs you.)
The graph appears here when the first command runs. The simulations are drawn by git-sim from a real repository.
The scrapbook picture appears as the story is told.
Level 7 complete
🎉 New rank unlocked
Branches are extra scrapbook sections that let programmers try out new storylines safely. git branch creates one. A branch is really just a marker for the latest page in a storyline of commits. The branch you are on is called the active branch, the checked-out branch, or simply the branch HEAD points to. Two branches share pages in their history, then diverge when new pages are added to each separately. Whew, that was a lot. See you in Level 8, where we put these storylines back together.
Get new levels and walkthroughs
New lessons and command walkthroughs, plus a Git trick or two. Your progress stays saved in this browser either way.
Free: the Git essentials cheat sheet
The 16 Git commands you'll use most, each with a picture of what it does to your repo, drawn by git-sim, on one printable sheet. Or pick your own 16. We'll email it to you, along with new levels and walkthroughs.