How git tracks commits in branches?

Question

I'm new to git and i've been exploring it since last month. I understand it's very powerful as compared to other version control system. Yesterday i learnt that git branches are just files that store the head(SHA1) of the commit as listed in .git/refs/heads/ directory. my question is : How does git track the whole branch by just one commit(SHA1)? When i do :

 `git show {SHA1}` 

it shows me that commit diff only. how does a commit knows which commit(s) is/are it's parents? When i do

`git rev-parse HEAD^1`

how does it shows me the commit which was before it. Initially i use to think a branch stores all of the commits involved in some specific order but now this fact has confused me totally.

Answer 1

Commits are stored as a Directed Acyclic Graph . If you have no merge commits in your history, then going back from a single branch head is equivalent to a linked list.

You can see the full contents of a commit by using:

git cat-file commit HEAD

The tree line refers to the contents of that commit (eg as seen by git ls-files ). Note that this is different than some other VCSes, which store deltas rather than trees.

The parent line(s), if any, are links to the previous commits.

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Generally, if you want this kind of low-level information, you should use commands listed under LOW-LEVEL COMMANDS (PLUMBING) in git 's man page.