Day 7 - Git and GitHub

🧠 1. What is Version Control System (VCS)?

A Version Control System (VCS) helps developers:

1. Share code efficiently among team members.

2. Track and manage changes (versions) in code over time.

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🧩 2. Why Do We Need Version Control?

🧍‍♂️ Problem 1 — Sharing Code

Example:

• Developer 1 writes addition functionality.

• Developer 2 writes subtraction functionality.

• Both must combine their work to build a calculator application.

In real projects (like Amazon or Flipkart), there are hundreds of files and dependencies.
Sharing and merging manually (through email, Slack, etc.) is impossible.

✅ VCS helps developers share and merge code safely and efficiently.

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🧾 Problem 2 — Versioning

Example:

• Initially: “Addition of 2 numbers”

• Later: “Addition of 3 numbers” → “Addition of 4 numbers”

• Finally: Product manager wants to revert to addition of 2 numbers.

Without versioning, you cannot roll back to an older working version.

✅ VCS lets you create, track, and revert code versions (v1, v2, v3, etc.).

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🧱 3. Types of Version Control Systems

🧩 Centralized Version Control (e.g., SVN, CVS)

• A single central server stores all code.

• Developers (Dev1, Dev2, etc.) commit and pull changes from that server.

• If the central server goes down → no one can collaborate.

 Dev1  ↔
        ↘
          Central Server (SVN)
        ↗
 Dev2  ↔

❌ Single point of failure
❌ Limited collaboration when offline

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🌍 Distributed Version Control (e.g., Git)

• Every developer has a full local copy of the repository.

• Developers can commit, work, and roll back locally.

• Later, changes can be pushed to a shared remote repository (e.g., GitHub).

       ┌──────────────┐
       │ Central Repo │
       └──────┬───────┘
              │
     ┌────────┴────────┐
     │                 │
 Local Repo 1     Local Repo 2
 (Dev1)             (Dev2)

✅ No single point of failure
✅ Work offline and sync anytime
✅ Faster operations

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💡 Interview Tip

Q: What is the difference between centralized and distributed VCS?
A: Centralized has one main server (like SVN); distributed gives each developer a full local copy (like Git).

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🔁 4. What is a Fork?

• A Fork is a personal copy of a repository.

• Developers use forks to make changes without affecting the original codebase.

Example:
Company’s main repo → example/project
Your fork → yourname/project

✅ You can modify freely and later merge back via a Pull Request.

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🧰 5. What is Git?

Git is an open-source distributed version control system.

• You can install Git on any server (e.g., EC2 instance or local machine).

• It tracks changes, manages versions, and supports collaboration.

• Commands like git add, git commit, and git push form the Git lifecycle.

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🌐 6. What is GitHub?

GitHub is a cloud-based platform built on top of Git that adds:

• UI and collaboration features

• Issue tracking

• Code reviews and pull requests

• CI/CD and project management tools

You can:

• Create repositories

• Host projects

• Collaborate with teams

• Manage workflows visually

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🧩 Git vs GitHub — Key Difference

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⚙️ 7. Installing Git

🔹 For Linux:

sudo apt update
sudo apt install git -y

🔹 For Windows/Mac:

Download from 👉 https://git-scm.com/downloads

✅ Verify installation:

git --version

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💻 8. Basic Git Lifecycle & Commands

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🧩 9. How Git Tracks Changes

• Git creates a hidden folder .git/ when you run git init.

• It contains:

  • objects/ → data storage (commits, blobs)

  • refs/ → references to branches

  • config → repository configuration

  • hooks/ → automation scripts

  • HEAD → pointer to current branch

If .git/ is deleted → repo tracking is lost.

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📘 10. Example Workflow

# Step 1: Create folder
mkdir example && cd example

# Step 2: Initialize Git
git init

# Step 3: Create a file
echo "a+b" > calculator.sh

# Step 4: Check status
git status

# Step 5: Track file
git add calculator.sh

# Step 6: Commit
git commit -m "Initial version - addition"

# Step 7: Modify file
echo "a+b+c" > calculator.sh

# Step 8: Check difference
git diff

# Step 9: Commit new version
git commit -am "Updated addition to include 3 numbers"

# Step 10: View commit history
git log

✅ You can revert to any previous version using:

git reset --hard <commit_id>

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☁️ 11. Connecting to GitHub

1. Create a GitHub account at https://github.com

2. Click New Repository

3. Name it → e.g., calculator

4. Choose Public or Private

5. Click Create Repository

Now connect your local repo:

git remote add origin https://github.com/<username>/<repo>.git
git branch -M main
git push -u origin main

Your project is now hosted on GitHub 🌍

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🧱 12. Real-World Collaboration Workflow

1. Fork the main repo (copy)

2. Clone to your local system

3. Make changes

4. Commit and push to your fork

5. Create a Pull Request (PR) to merge into the main branch

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🧩 13. Summary

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✅ In short:

Git manages your code versions locally.
GitHub lets you share and collaborate globally.