Version ControlIntermediate

Git & Version Control Mastery

Git is a content-addressable directed acyclic graph (DAG) storage system disguised as a version control tool.

Key Mental Models & Invariants

  • -Commits are immutable snapshots, referenced by SHA-1/SHA-256 hashes.
  • -Branches are nothing more than 41-byte pointer files containing a commit hash.
  • -HEAD is a reference indicating what commit/branch you are currently working on.
  • -Merge combines histories preserving chronologic graph nodes; Rebase rewrites history linearly.
  • -The 3-tree model: Working Directory -> Staging Area (Index) -> Repository (HEAD).

Deep Dive Architecture

### The 3 Trees of Git Git does not store diffs; it stores **snapshots**. When you run: 1. `git add <file>`: Git computes the SHA-1 of the file content, compresses it into a blob in `.git/objects`, and records the path & hash in the **Index** (Staging Area). 2. `git commit -m "msg"`: Git writes a tree object representing the directory structure, creates a commit object pointing to that tree and the parent commit, and moves the current branch pointer forward. ```text Working Directory Staging Area (Index) Local Repo (.git) ┌─────────────────┐ ┌────────────────────┐ ┌───────────────────┐ │ modified files │ ───> │ git add . │ ───> │ git commit │ │ on your disk │ │ prepared snapshot │ │ immutable commit │ └─────────────────┘ └────────────────────┘ └───────────────────┘ ``` ### Merge vs Rebase - **Merge**: Creates a new "merge commit" with 2 parents. Completely non-destructive, preserves exact historical context. - **Rebase**: Replays your branch commits one by one on top of the target branch, creating new commits with new hashes. Results in a clean, linear git log. 

      Feature:      C --- D
                   /
Main:   A --- B ----------- M (Merge Commit)
                   \       /
                    (or Rebase: A --- B --- C' --- D')
Code Examplebash
# Undo last commit without losing changes on disk
git reset --soft HEAD~1

# Stash untracked files too
git stash -u

# Interactive rebase last 3 commits
git rebase -i HEAD~3

Soft reset unwinds the commit object back to the staging area. git stash -u stashes uncommitted and untracked files.