Git Basics and GitHub Introduction¶

What is Git?¶

Git is a free, open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency. Created by Linus Torvalds in 2005 for Linux kernel development.

About Git - GitHub's Git overview Git Documentation - Official Git reference

Key Characteristics¶

• Distributed - Every developer has a full copy of the repository
• Fast - Most operations are local and nearly instantaneous
• Data integrity - Every file and commit is checksummed (SHA-1)
• Branching model - Lightweight, fast branching and merging
• Staging area - Intermediate area for preparing commits

Git vs Other VCS¶

Git Architecture¶

The Three Trees¶

1. Working Directory - Files you see and edit on disk
2. Staging Area (Index) - Changes marked for the next commit
3. Repository (.git) - Committed snapshots stored in Git's database

Working Directory --> Staging Area --> Repository
    (git add)         (git commit)

File States¶

• Untracked - New files Git does not know about
• Modified - Changed files not yet staged
• Staged - Modified files marked for the next commit
• Committed - Safely stored in the local repository

Recording Changes - File lifecycle

Essential Git Commands¶

Repository Setup¶

# Initialize a new repository
git init

# Clone an existing repository
git clone https://github.com/user/repo.git

# Clone to a specific directory
git clone https://github.com/user/repo.git my-folder

Creating a Repository - Repository creation guide

Basic Workflow¶

# Check status of working directory
git status

# Stage specific files
git add file.txt

# Stage all changes
git add .

# Commit staged changes
git commit -m "Add login feature"

# View commit history
git log
git log --oneline --graph

Branching¶

# List branches
git branch

# Create a new branch
git branch feature-branch

# Switch to a branch
git checkout feature-branch
git switch feature-branch    # newer syntax

# Create and switch in one command
git checkout -b feature-branch
git switch -c feature-branch  # newer syntax

# Delete a branch
git branch -d feature-branch

About Branches - Branch concepts

Merging¶

# Merge a branch into current branch
git merge feature-branch

# Merge with a merge commit (no fast-forward)
git merge --no-ff feature-branch

# Abort a merge with conflicts
git merge --abort

Rebasing¶

# Rebase current branch onto main
git rebase main

# Interactive rebase (squash, edit, reorder commits)
git rebase -i HEAD~3

# Abort a rebase
git rebase --abort

Key difference: Merge preserves history with a merge commit; rebase replays commits for linear history.

Remote Operations¶

# View remote repositories
git remote -v

# Add a remote
git remote add origin https://github.com/user/repo.git

# Fetch changes (download only, no merge)
git fetch origin

# Pull changes (fetch + merge)
git pull origin main

# Push changes to remote
git push origin main

# Push a new branch
git push -u origin feature-branch

Getting Changes from a Remote - Remote operations

Critical Difference: Fetch vs Pull¶

Undoing Changes¶

# Unstage a file (keep changes)
git reset HEAD file.txt

# Discard changes in working directory
git checkout -- file.txt
git restore file.txt          # newer syntax

# Undo last commit (keep changes staged)
git reset --soft HEAD~1

# Undo last commit (keep changes unstaged)
git reset --mixed HEAD~1

# Undo last commit (discard changes)
git reset --hard HEAD~1

# Create a new commit that undoes a previous commit
git revert <commit-hash>

Other Useful Commands¶

# Show changes
git diff                    # working directory vs staging
git diff --staged           # staging vs last commit

# Temporarily save changes
git stash
git stash pop               # restore and remove from stash
git stash list              # view stashed changes

# View file history
git blame file.txt          # who changed each line

# Search commits
git log --grep="bug fix"    # search commit messages

Merge Conflicts¶

When Do They Occur?¶

• Two branches modify the same line(s) in the same file
• One branch deletes a file that the other branch modified
• Both branches add a file with the same name but different content

Conflict Markers¶

<<<<<<< HEAD
Your changes (current branch)
=======
Their changes (incoming branch)
>>>>>>> feature-branch

Resolving Conflicts¶

1. Open the conflicted file
2. Choose which changes to keep (or combine both)
3. Remove the conflict markers (<<<<<<<, =======, >>>>>>>)
4. Stage the resolved file with git add
5. Complete the merge with git commit

Resolving Merge Conflicts - Conflict resolution guide

What is GitHub?¶

GitHub is a cloud-based platform built on top of Git that provides: - Repository hosting - Store and share code remotely - Collaboration - Issues, pull requests, code review - Automation - GitHub Actions for CI/CD - Security - Dependabot, secret scanning, code scanning - Project management - Projects, milestones, labels - Community - Open source hosting, Sponsors, Discussions

About GitHub and Git - Platform overview

GitHub Account Types¶

• Personal account - Individual user, owns repositories
• Organization account - Shared account for teams, owns repositories, manages teams
• Enterprise account - Manages multiple organizations with centralized policies

Types of GitHub Accounts - Account types

GitHub Plans¶

GitHub Plans - Plan comparison

GitHub Tools¶

• GitHub.com - Web interface for all GitHub features
• GitHub Desktop - GUI for Git operations (Windows, macOS)
• GitHub Mobile - iOS/Android app for on-the-go management
• GitHub CLI (gh) - Command-line tool for GitHub operations
• GitHub Codespaces - Cloud-hosted development environments

GitHub CLI - CLI documentation GitHub Desktop - Desktop app guide GitHub Mobile - Mobile app features

GitHub Markdown¶

GitHub uses GitHub Flavored Markdown (GFM) for formatting text in issues, PRs, READMEs, and more.

Essential Syntax¶

# Heading 1
## Heading 2

**bold** and *italic* and ~~strikethrough~~

- Unordered list
1. Ordered list
- [ ] Task list item

[Link text](url)
![Image alt text](image-url)

`inline code`

> Blockquote

| Column 1 | Column 2 |
|----------|----------|
| Cell 1   | Cell 2   |

GitHub-Specific Features¶

• @mentions for users and teams
• #references for issues and PRs
• Emoji shortcodes ()
• Mermaid diagrams in code blocks
• Mathematical expressions with LaTeX
• Alerts: > [!NOTE], > [!WARNING], > [!IMPORTANT]

Basic Formatting Syntax - Markdown reference GitHub Flavored Markdown Spec - GFM specification

Key Exam Points¶

• Git is distributed - every clone is a full repository
• The staging area is what makes Git unique among VCS
• git fetch never changes your working directory; git pull does
• Merge creates a merge commit; rebase creates linear history
• git reset modifies history; git revert creates new commits
• GitHub is a platform built on Git, not a replacement for Git
• Know the difference between Personal, Organization, and Enterprise accounts
• GitHub Free includes unlimited public AND private repositories