Git overview

Lots of different coders often work on the same project, from different computers, sometimes from all around the world. With just one copy of the code, or worse, a copy per person, that gets messy fast.

Who changed line one? When did this break? Which of these five copies is the newest? Coders need a way to make their own changes, share them, and keep track of what changed, when it changed and who changed it.

In other words, they need a SYSTEM... to CONTROL... the VERSIONS... of the code. See what happened there? Git is the version control system, or VCS, that most coders use.

Git keeps track of which code files were changed, which lines were edited, who made each change and when. That builds up a full history of your code from day one to today, so you can see how the project changed over time, share code with others, combine everyone's changes, and find out what went wrong when something breaks.

Every level has a picture on the left and a story on the right. Sometimes the picture is the scrapbook: a homemade book where memories get stuck onto pages. It stands in for Git, and each part of it is one Git idea. You will meet those parts one at a time, starting in Level 2.

Sometimes the picture is a graph: a drawing of a real repository, made by a tool called git-sim while the real commands ran. You can drag its slider to watch a command play out, hover things to see what they are, and press Enlarge when you want it bigger.

Above the graph sits a terminal. When a step has a command, you type it there yourself, the way you would on your own computer. Get it right and the graph plays the command from before to after, with the exact output Git printed. Get it wrong and the terminal tells you what is off, as many times as it takes. Now and then a level stops and asks you to choose a command instead: every option is worth trying, because the picture shows what each choice would have done.

Here is a sneak peek: the repository you will have built by the end of Level 16, drawn by git-sim. Every circle is a change you will make yourself. Every label is a word you will know. Ask Git for the log, its list of every page:

You do not need to understand any of it yet. Just notice that it is a chain of connected steps with a few labels on it, and that nothing here is a drawing of an idea. It is the real thing, read straight from the repository.