Git Fundamentals

# === Setup (do once per machine) ===
git config --global user.name  "Your Name"
git config --global user.email "you@example.com"
git config --global core.editor "code --wait"
git config --global init.defaultBranch main
git config --list              # Verify config

# === Start a project ===
git init                       # New repo in current dir
git clone https://github.com/user/repo.git
git clone repo.git my-dir      # Clone into custom dir

# === See what's happening ===
git status                     # Untracked / modified / staged
git diff                       # Unstaged changes (vs last commit)
git diff --staged              # Staged changes (what will be committed)
git diff HEAD~1                # Changes since last commit

# === Stage + commit ===
git add file.txt               # Stage specific file
git add .                      # Stage ALL changes (use carefully)
git add -p                     # Interactive: choose hunks to stage
git commit -m "feat: add login"
git commit --amend             # Fix last commit message (before push)

# === Undo ===
git restore file.txt           # Discard working dir changes
git restore --staged file.txt  # Unstage (keep changes in working dir)
git reset HEAD~1               # Undo last commit (keep changes staged)
git revert abc123              # Safe undo — creates a new "undo commit"

# === SECRETS (NEVER commit these) ===
.env
.env.local
.env.*.local
*.pem
*.key
*_rsa
*_dsa
secrets.yml
credentials.json

# === Node.js ===
node_modules/
dist/
build/
.npm
npm-debug.log*
yarn-error.log

# === Python ===
__pycache__/
*.pyc
*.pyo
.venv/
venv/
*.egg-info/

# === OS / IDE ===
.DS_Store         # macOS
Thumbs.db         # Windows
.idea/            # IntelliJ
.vscode/          # VS Code (optional)
*.swp             # Vim swap files

# === Docker ===
*.dockerignore    # Already handled by Docker

# === Terraform ===
.terraform/
*.tfstate
*.tfstate.backup
*.tfvars          # May contain secrets

# === Logs + Temp ===
*.log
*.tmp
coverage/
.nyc_output/

# === diff ===
git diff                    # Working dir vs last commit
git diff --staged           # Staged vs last commit
git diff main feature-x     # Between two branches
git diff HEAD~3 HEAD -- app.js  # One file, 3 commits back

# === stash — save incomplete work ===
# Scenario: mid-feature, urgent hotfix needed
git stash push -m "WIP: user dashboard"
git checkout main           # Switch to main for hotfix
# ... fix the bug, commit, push ...
git checkout feature/dashboard
git stash pop               # Restore your work

# === Useful aliases — add to ~/.gitconfig ===
git config --global alias.st  "status -sb"
git config --global alias.lg  "log --oneline --graph --all --decorate"
git config --global alias.cm  "commit -m"
git config --global alias.aa  "add -A"
git config --global alias.undo "reset HEAD~1"

# Now you can use:
git st        # Short status
git lg        # Pretty graph log
git undo      # Undo last commit

# === Show file history ===
git log --follow -p src/auth.js  # All commits that touched this file
git blame src/auth.js            # Who wrote each line
git log --all --full-history -- "*.secret"  # Find deleted file history

# === 1. Configure Git ===
git config --global user.name  "Your Full Name"
git config --global user.email "you@example.com"
git config --global core.editor "code --wait"
git config --global init.defaultBranch main
git config --global alias.lg "log --oneline --graph --all --decorate"
git config --global alias.st "status -sb"

# === 2. Create project ===
mkdir my-devops-app && cd my-devops-app
git init
echo "# My DevOps App" > README.md
echo "A sample app built during the DevOps 35-day course." >> README.md

# === 3. First commit ===
git status
git add README.md
git status             # See it go from red to green
git commit -m "feat: initial project setup with README"
git log --oneline

# === 4. Add .gitignore ===
cat > .gitignore << 'EOF'
node_modules/
.env
*.log
dist/
.DS_Store
.vscode/
EOF
git add .gitignore
git commit -m "chore: add gitignore for Node.js project"

# === 5. Create package.json ===
cat > package.json << 'EOF'
{
  "name": "my-devops-app",
  "version": "1.0.0",
  "description": "DevOps 35-day course app"
}
EOF
git add package.json
git commit -m "chore: add package.json"
git log --oneline      # Should show 3 commits

[user]
	name  = Your Full Name
	email = you@example.com

[core]
	editor      = code --wait
	autocrlf    = input      # Linux/Mac: input | Windows: true
	whitespace  = trailing-space,space-before-tab

[init]
	defaultBranch = main

[pull]
	rebase = true             # Always rebase on pull

[push]
	autoSetupRemote = true    # Auto -u on first push

[fetch]
	prune = true              # Remove deleted remote branches

[merge]
	conflictstyle = diff3     # Show base + both sides in conflicts

[diff]
	colorMoved = zebra

[alias]
	st   = status -sb
	lg   = log --oneline --graph --all --decorate
	cm   = commit -m
	aa   = add -A
	undo = reset HEAD~1
	hide = stash push -m

[color]
	ui = auto

# Inside any git repo, run:
ls -la .git/
# .git/
# ├── HEAD          ← which branch/commit you're on
# ├── config        ← repo-level git config
# ├── index         ← the staging area (binary)
# ├── objects/      ← all commits, trees, blobs (compressed)
# └── refs/
#     ├── heads/    ← local branches (just text files with SHA)
#     └── remotes/  ← remote tracking branches

# See what HEAD points to:
cat .git/HEAD
# ref: refs/heads/main

# See what main branch points to:
cat .git/refs/heads/main
# a3f7c2d1e4b5... (the SHA of the latest commit)

# Read a commit object:
git cat-file -p HEAD
# tree abc123...    ← snapshot of all files
# parent def456...  ← previous commit
# author ...
# committer ...

# Git objects are content-addressed storage:
# SHA = hash of content. Same content = same SHA.
# This is why Git is reliable — nothing can silently change.