git commit — Saving Snapshots

git commit permanently saves your staged changes as an immutable snapshot in history. Each commit gets a unique SHA-1 hash, stores your name, email, timestamp, message, and a pointer to the parent commit.

01.Anatomy of a Good Commit Message

Write commit messages in imperative mood, present tense: "Add login form" not "Added login form". Keep the subject line under 72 characters. Add a blank line, then a body explaining WHY (not what — the diff shows what). Reference issue numbers: "Fix crash on logout (closes #42)".

Commit Timeline

a1b2c3d

init

b2c3d4e

feat

c3d4e5f

fix

d4e5f6a

HEAD

02.Commits Are Snapshots, Not Diffs

Git stores complete file snapshots per commit — not just what changed. This makes operations like branch switching instantaneous regardless of history length. The diff you see in git log is computed on-the-fly by comparing two consecutive snapshots.

Git's Three Areas

📁

Working Dir

Your files

→ git add

📋

Staging Area

Prepared

→ git commit

🗄️

Repository

.git/ history

Commands

commands — click to reveal output

git commit -m "Add user authentication"

Commit staged files with an inline message

git commit

Open your text editor to write a detailed multi-line message

git commit -am "Fix typo in README"

Stage all tracked modified files AND commit in one step

git commit --amend -m "Better message"

Rewrite the last commit message (only before pushing!)

git log --oneline

View compact commit history

▼ show output

KNOWLEDGE CHECK

What does Git store in each commit object?

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