How to Work with Branches in Git — Under the Hood 관련

A Visual Guide to Git Internals — Objects, Branches, and How to Create a Repo From Scratch

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Many of us use git on a daily basis. But how many of us know what goes on under the hood? For example, what happens when we use git commit? What is stored between commits? Is it just a diff between the current and previous commit? If so, how

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A Visual Guide to Git Internals — Objects, Branches, and How to Create a Repo From Scratch

Many of us use git on a daily basis. But how many of us know what goes on under the hood? For example, what happens when we use git commit? What is stored between commits? Is it just a diff between the current and previous commit? If so, how

Just as we’ve created a repository and a commit without using git init, git add or git commit, now we will create and switch between branches without using porcelain commands (git branch or git checkout).

It’s perfectly understandable if you are excited, I am too 🙂

Let’s start:

So far we only have one branch, named master. To create another one with the name test (as the equivalent of git branch test), we would need to simply create a file named test within .git\refs\heads, and the contents of that file would be the same commit’s hash as the master points to.

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If we use git log, we can see that this is indeed the case

both master and test point to this commit

Let’s also switch to our newly created branch (the equivalent of git checkout test). For that, we should change HEAD to point to our new branch:

Switching to branch test by changing HEAD

As we can see, both git status and git log confirm that HEAD now points to test, which is, therefore, the active branch.

We can now use the commands we have already used to create another file and add it to the index

Using the commands above, we have created a file named test.txt, with the content of Testing, created a corresponding blob, and added it to the index. We also created a tree representing the index.

It’s now time to create a commit referencing this tree. This time, we should also specify the parent of this commit — which would be the previous commit. We specify the parent using the -p switch of git commit-tree:

We have just created a commit, with a tree as well as a parent, as we can see

Will git log show us the new commit?

As we can see, git log doesn’t show anything new. Why is that? 🤔 Remember that git log traces the branches to find relevant commits to show. It shows us now test and the commit it points to, and it also shows master which points to the same commit.

That’s right — we need to change test to point to our new commit. We can do that by simply changing the contents of .git\refs\heads\test:

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It worked! 🎉🥂

git log goes to HEAD, which tells it to go to the branch test, which points to commit 465...5e, which links back to its parent commit 80e...8f.

Feel free to admire the beauty, we git you. 😊