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lab 22 Git Internals:
The .git directory

Goals

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	ORIG_HEAD	hooks		logs		rr-cache
HEAD		config		index		objects
MERGE_RR	description	info		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
09	24	43	6b	94	af	dd	e7	info
11	27	59	78	97	b5	e1	ef	pack
19	28	69	7b	9c	c4	e4	f6

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/09
6b74c56bfc6b40e754fc0725b8c70b2038b91e	9fb6f9d3a104feb32fcac22354c4d0e8a182c1

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 = Jim Weirich
	email = jim (at) edgecase.com

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
master
$ ls .git/refs/tags
v1
v1-beta
$ cat .git/refs/tags/v1
7bf0bf17ab217ae2415f16aaddc55d0ee1d1db8e

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 master in this directory.

The HEAD File

Execute:

cat .git/HEAD

Output:

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

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