Git Immersion

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lab 20 Git Internals:
The .git directory

Goals

• Learn about the structure of the .git directory

The .git Directory

Time to do some exploring. First, from the root of your project directory…

Execute:

ls -C .git

Output:

$ ls -C .git
COMMIT_EDITMSG	config		index		objects
HEAD		description	info		packed-refs
ORIG_HEAD	hooks		logs		refs

This is the magic directory where all the git “stuff” is stored. Let’s peek in the objects directory.

The Object Store

Execute:

ls -C .git/objects

Output:

$ ls -C .git/objects
03	31	75	82	98	aa	db	e4	fa
0b	5e	7a	83	9a	bb	df	e5	info
1c	69	80	8a	a8	d3	e3	e9	pack

You should see a bunch of directories with 2 letter names. The directory names are the first two letters of the sha1 hash of the object stored in git.

Deeper into the Object Store

Execute:

ls -C .git/objects/<dir>

Output:

$ ls -C .git/objects/03
d4fb6fb12c30fc41b68f7f6b64eb1ee6945bdb

Look in one of the two-letter directories. You should see some files with 38-character names. These are the files that contain the objects stored in git. These files are compressed and encoded, so looking at their contents directly won’t be very helpful, but we will take a closer look in a bit.

Config File

Execute:

cat .git/config

Output:

$ cat .git/config
[core]
	repositoryformatversion = 0
	filemode = true
	bare = false
	logallrefupdates = true
	ignorecase = true
	precomposeunicode = true
[user]
	name = Théophile Chevalier
	email = [email protected]

This is a project-specific configuration file. Config entries in here will override the config entries in the .gitconfig file in your home directory, at least for this project.

Branches and Tags

Execute:

ls .git/refs
ls .git/refs/heads
ls .git/refs/tags
cat .git/refs/tags/v1

Output:

$ ls .git/refs
heads
tags
$ ls .git/refs/heads
main
$ ls .git/refs/tags
v1
v1-beta
$ cat .git/refs/tags/v1
1c410c657e8ba922365b4f5c5b5f42f60bb08798

You should recognize the files in the tags subdirectory. Each file corresponds to a tag you created with the git tag command earlier. Its content is just the hash of the commit tied to the tag.

The heads directory is similar, but is used for branches rather than tags. We only have one branch at the moment, so all you will see is main in this directory.

The HEAD File

Execute:

cat .git/HEAD

Output:

$ cat .git/HEAD
ref: refs/heads/main

The HEAD file contains a reference to the current branch. It should be a reference to main at this point.