git init

Published on September 28th, 2019

Introduction

One interesting feature with git is that its entire state is stored on your machine, inside the .git directory of your repository.

That means that, by observing what is happening in that .git directory, you can understand what git is trying to do when you type all those pesky commands.

git init

Let’s start with the command to create a local repository: git init

$ git init
Initialized empty Git repository in <your directory>/.git/

This command creates quite a few files inside this .git directory:

HEAD
config
description
hooks/applypatch-msg.sample
hooks/commit-msg.sample
hooks/fsmonitor-watchman.sample
hooks/post-update.sample
hooks/pre-applypatch.sample
hooks/pre-commit.sample
hooks/pre-push.sample
hooks/pre-rebase.sample
hooks/pre-receive.sample
hooks/prepare-commit-msg.sample
hooks/update.sample
info/exclude

We’ll have a look to all those files in subsequent posts, but for now will focus only on 3 types of files:

  • the commits which are stored in the .git/objects directory
  • the references stored in the refs directory
  • the symbolic references like the HEAD file

At this stage, there is only one of those files: the HEAD file which contains:

ref: refs/heads/master

This is a link to a reference which doesn’t exist as we don’t have any commits yet…

our first commit

Let’s create our first commit:

$ echo "hello" > hello.txt
$ git add hello.txt
$ git commit -m 'say hello'
[master (root-commit) f1628af] say hello
 1 file changed, 1 insertion(+)
 create mode 100644 hello.txt

Tada! we have our first commit and a reference which points to that commit.Nothing too crazy here. Time for a second commit.

Nothing too crazy here. Time for a second commit.

$ echo "how are you doing?" > greet.txt
$ git add greet.txt
$ git commit -m 'be friendly'
[master 7f03bd8] be friendly
 1 file changed, 1 insertion(+)
 create mode 100644 greet.txt

We already see a pattern:

  • the new commit has a parent reference to the previous one
  • the ref/heads/master reference is updated to point to our new commit
  • HEAD keeps the same value which means it also points to the last commit

The process will repeat with our 3rd commit.

$ echo "bye" > bye.txt
$ git add bye.txt
$ git commit -m 'say bye'
[master eb3562c] say bye
 1 file changed, 1 insertion(+
 create mode 100644 bye.txt

As expected, the commit tree is:

Nothing too exciting yet, but we’ll see what happens when we create new branches or connect to a remote repository.