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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
06	18	28	44	69	8c	9c	c4	e4	info
09	24	42	4d	6b	97	af	d5	e7	pack
11	27	43	59	78	9a	b5	dc	ed

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/06
3b40ead4efa2dce10ca893772c83483f0b546b

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
4d578d47c426d4d94fcb3c645fe29c27138f3900

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.