git-under-the-hood.txt

LOOKING at .git FOLDER
mkdir testing1 && cd testing1
git init
(Split vertically -- tree .git)
************ watch -n 1 'tree .git/objects'
echo "Hello world" > hello.txt
git add hello.txt
cat .git/objects/80/2992c4220de19a90767f3000a79a31b98d0df7
*********** alias deflate="perl -MCompress::Zlib -e 'undef $/; print uncompress(<>)'" 
deflate .git/objects/80/2992c4220de19a90767f3000a79a31b98d0df7
printf "blob 12\000Hello world\n" | shasum

(SLIDES)

COMMITS -> TREES -> BLOBS
git ls-files -s
git commit -m "First commit"
(tree .git)
git cat-file -t ef866f30a61b24b38a650c22223bf4a62fb9a6fb
git cat-file -t a50b30eb6b223aef893c367a0b93e9a5b21f155f
git cat-file -p ef866f30a61b24b38a650c22223bf4a62fb9a6fb
git cat-file -p a50b30eb6b223aef893c367a0b93e9a5b21f155f

(SLIDES)

CHANGING AN EXISTING COMMITTED FILE'S CONTENT
echo "Hello Git" > hello.txt
git add hello.txt
git commit -m "Change text"
git cat-file -p 552af3101d23cd029114ae07708f0b3228b4ea5f
git cat-file -p 2f092e9cadfc1eb4a6d2febfddb941f4c1fe6fd6
git cat-file -p 9f4d96d5b00d98959ea9960f069585ce42b1349a
git log -p

COMMITTING A SECOND FILE
echo "More text" > second.txt
git add second.txt
git commit -m "Add second.txt"
*tree we just created* — git cat-file -p head^{tree}
*tree in the prior commit* — git cat-file -p head^^{tree}

COMMITTING A SUBFOLDER WITH A FILE OF THE SAME CONTENT
mkdir subfolder
echo "Hello Git" > subfolder/subfile.txt
git add subfolder
git commit -m "Add subfolder"
git cat-file -p head^{tree}
git cat-file -p head^^{tree}
git cat-file -p 58f663278d381fb6be12b6e110b7580fbde8ab9d

(Slides)

REFS, BRANCHES, HEAD, and TAGS
BRANCHES
************ watch -n 1 'tree .git -I "hooks|objects"'
cat .git/refs/heads/master
glol
git rev-parse master~1
git rev-parse master~1 > .git/refs/heads/newbranch
git branch
git checkout newbranch
git checkout master
echo “Even more text" > third.txt
git add third.txt
git commit -m "Add third.txt"
glol

HEAD
cat .git/HEAD
git checkout head~1 (detached head state)
cat .git/HEAD
git checkout newbranch
cat .git/HEAD
echo 'ref: refs/heads/master' > .git/HEAD
echo "Keep adding text" > fourth.txt
git add fourth.txt
git commit -m "Add fourth.txt"
cat .git/HEAD

TAGS
git tag mytag
cat .git/refs/tags/mytag
git cat-file -t 6502f980a3ce9c749e4df0a837ca5f62f4fb65bd
git tag -a v1.0.0-alpha
cat .git/refs/tags/v1.0.0-alpha
git cat-file -t 5bec469f65868e8a0728d1a5ccf103f2a1253fb3
git cat-file -p 5bec469f65868e8a0728d1a5ccf103f2a1253fb3