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Git

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Git is a free and open source distributed version control system designed for speed, correctness, and support for non-linear development. Linus Torvalds created it in 2005 to manage Linux kernel contributions after the team lost access to BitKeeper. The core design decision: every developer holds a full copy of the repository history, not just a working copy checked out from a server.

Internally, Git represents history as a directed acyclic graph of commit objects. Each commit points to its parent(s), a tree object (representing the directory snapshot), and carries author, committer, and message metadata. Branches are lightweight pointers to commits, not copies of files.

Core Concepts

Repository: A directory tracked by Git, containing the full history of all commits, branches, and tags in a hidden .git/ folder.

Staging area (index): A buffer between the working directory and the next commit. git add stages changes selectively, allowing a single commit to be composed from partial file changes.

Commit: An immutable snapshot of the entire repository tree at a point in time. Git identifies commits by their SHA-1 (now SHA-256 in newer repos) hash, computed from content, not filenames or timestamps.

Branch: A named pointer to a commit. Creating a branch is nearly instant because it only creates a 41-byte file. HEAD is a special pointer that tracks which branch you are currently on.

Remote: A reference to another copy of the repository (GitHub, a coworker’s machine, a bare server). Remotes are just named URLs; origin is convention, not magic.

Essential Commands

# Start and inspect
git init                      # Initialize a new repo
git clone <url>               # Clone a remote repo locally
git status                    # Show working tree and staging state
git log --oneline --graph     # Visual commit history
 
# Stage and commit
git add <file>                # Stage a file
git add -p                    # Stage interactively, hunk by hunk
git commit -m "message"       # Commit staged changes
git commit --amend            # Rewrite the last commit (before push only)
 
# Branch and merge
git branch <name>             # Create a branch
git switch <name>             # Switch to a branch (modern form)
git merge <branch>            # Merge a branch into HEAD
git rebase <branch>           # Replay commits onto a new base
 
# Collaborate
git fetch                     # Download remote changes without merging
git pull                      # fetch + merge (or fetch + rebase with --rebase)
git push origin <branch>      # Push a branch to the remote

Workflow Patterns

Feature branch: Each feature or fix lives on its own branch, merged into main via pull request. Keeps main stable; standard on GitHub-hosted projects.

Trunk-based development: All developers commit directly to main (or very short-lived branches). Requires feature flags for incomplete work. Scales well for continuous deployment.

Gitflow: Formalizes long-lived develop and release branches. Suits projects with scheduled releases and multiple active version lines. Adds ceremony that trunk-based avoids.

Email-driven: Patches formatted with git format-patch and mailed to a list; maintainer applies with git am. Used by the Linux kernel and the Git project itself. See Git Send-Email.

  • GitHub: cloud hosting platform built on Git; adds pull requests, Actions, and issue tracking
  • Git Send-Email: the original email-driven patch contribution workflow
  • Changelog: conventions for documenting what changed across versions
  • Version Control

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