What Really Happens Inside Git When You Init, Add, Commit, and Branch?

Git Init and .git Directory Structure

Running git init creates a .git folder that contains all metadata needed for version control, including HEAD , config , description , hooks , info , objects , and refs .

# left side execution
mkdir git-demo
cd git-demo && git init
rm -rf .git/hooks/*.sample

# right side execution
watch -n 1 -d find .

.git Directory Contents

.git/config – local repository configuration file

.git/objects – stores objects (blobs, commits, trees)

.git/info – exclusion information

.git/hooks – default hook scripts

.git/HEAD – pointer to the current branch

.git/refs – pointers to branch heads and tags

tree .git
.git
├── HEAD
├── config
├── description
├── hooks
├── info
│   └── exclude
├── objects
│   ├── info
│   └── pack
└── refs
    ├── heads
    │   ├── dev
    │   ├── master
    │   └── tmp
    └── tags

Understanding git add and Blob Objects

When git add is executed, Git creates a blob object that stores the file’s content and type, but not its name. The blob’s SHA‑1 hash is calculated as blob <size>\0<content>. Identical file contents share the same blob.

# left side execution
echo "hello git" > hello.txt
git status
git add hello.txt

# right side execution
watch -n 1 -d find .

The resulting object can be inspected:

git cat-file -t 8d0e41   # shows "blob"
git cat-file -p 8d0e41   # shows file content
git cat-file -s 8d0e41   # shows size (10 bytes)

Index (Staging Area)

The index file records file names and references to their blob objects. Commands like git ls-files -s display the staged entries.

git ls-files -s

Commit Objects and Tree Structure

Executing git commit creates a commit object that references a tree object (the snapshot of the project) and parent commits. The tree object contains entries for files (blobs) and sub‑directories (sub‑trees).

# left side execution
git commit -m "1st commit"

git cat-file -t 6e4a700   # shows "commit"
git cat-file -p 6e4a700   # displays commit metadata

git cat-file -t 64d6ef5   # shows "tree"
git cat-file -p 64d6ef5   # displays tree entries

HEAD and Branch Pointers

HEAD always points to the current branch’s latest commit. Branches are simple pointers stored under .git/refs/heads . Creating a branch with git branch dev adds dev under refs/heads . Switching branches updates HEAD to point to the new branch.

git branch dev
cat .git/refs/heads/dev   # shows commit hash
cat .git/HEAD              # shows "ref: refs/heads/master"
git checkout dev
cat .git/HEAD              # now shows "ref: refs/heads/dev"

Remote Repositories and Pushing

To link a local repository with a remote server:

git remote add origin [email protected]:escapelife/git-demo.git

The remote configuration appears in .git/config under a [remote "origin"] section. Pushing the local master branch to the remote creates corresponding refs under .git/refs/remotes/origin .

git push -u origin master

Remote Tracking Structure

tree .git
├── logs
│   ├── HEAD
│   └── refs
│       ├── heads
│       │   ├── dev
│       │   ├── master
│       │   └── tmp
│       └── remotes
│           └── origin
│               └── master
└── refs
    ├── heads
    │   ├── dev
    │   ├── master
    │   └── tmp
    └── remotes
        └── origin
            └── master

Recovering Lost Commits

Even after deleting a branch, its commits remain reachable via git reflog, which records all reference updates.

git reflog
git checkout 9fb7a14   # restore a lost commit
git checkout -b dev

Diff Logic

Git compares the SHA‑1 hashes of blobs in the index versus the working tree to generate diffs. Commands like git diff, git diff --cached, and git diff HEAD show changes at different stages.

echo "hello" > file1.txt
git diff
git diff --cached
git diff HEAD

Summary of File Lifecycle

Files move between three areas: the working directory, the index (staging area), and the repository (committed snapshots). Git tracks their state using blob objects, tree objects, and commit objects, while branch pointers and HEAD manage the current context.