Video from #LvivJavaClub event

Agenda

Intro. Git as a file system.

Git efficiency examples (storage, network)

Create an empty directory. Show that it's not a goit repo (git status)

Create .git dir. Show that it's not a goit repo (git status)

Create objects, refs/heads, refs/tags folders, and HEAD file. Show that it's not a git repo (git status)

add the following line to HEADS: ref: refs/heads/master. Run git status

Blobs. git hash-object examples:

1. echo "git is awesome" | git hash-object --stdin
2. git hash-object <filename>,
3. add -w, show contents of .git/objects folder. Explain directories naming
4. write an identical file and show that the hash is the same
5. write a different file, show that the hash is different, and show another blob in the repository

git cat-file, -t (type), and -p (pretty-print) options

Explain concepts:

1. working directory
2. index/cache/staging area
3. repository

Add to index:

1. create a subfolder, and add file to the subfolder
2. git update-index --add --cacheinfo 100644 <blob-hash> <filename> and variations:
   1. existing file (previously written to a repo with git has-object -w)
   2. non-existing file,
   3. existing file but with content different that in the blob

Tree:

1. create an untracked file (don't add it to the index)
2. git write-tree
3. git cat-file for the created tree

Commits:

1. create commit: git commit-tree <tree-hash> -m <commit message>
2. git cat-file for commit
3. create a commit with a parent commit
4. Explain that git history is a snapshot of the state of the tree, not a sequence of diffs

Branches, HEAD:

1. create 2 branches by creating 2 files in .git/refs/heads folder. Point branches to specific commits
2. change the reference in the HEAD file to another branch. Show the result with git branch
3. Summary: branches and HEAD are just references (as well as tags)

git fsck

Show visual learning tools:

1. http://git-school.github.io/visualizing-git/ 16. Demonstrate merge vs rebase
2. https://learngitbranching.js.org

Alternative (non-SCM) git use cases

Additional Resources

https://github.com/pluralsight/git-internals-pdf

https://blog.thoughtram.io/git/2014/11/18/the-anatomy-of-a-git-commit.html

https://jwiegley.github.io/git-from-the-bottom-up/1-Repository/5-the-beauty-of-commits.html

https://www.freecodecamp.org/news/git-internals-objects-branches-create-repo/

https://aboullaite.me/deep-dive-into-git/

https://gitolite.com/uses-of-index.html

https://www.chromium.org/developers/fast-intro-to-git-internals

https://www.tutorialspoint.com/what-is-3-way-merge-or-merge-commit-in-git