Git Master Guide 🚀

This documentation covers essential Git workflows, configurations (PAT & SSH), and advanced usage tips including hooks and multi-account SSH setups.

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📁 Git Concepts & Workflow

Git Directory Structure

• Working Directory: Your local files.
• Staging Area (Index): Files prepared for the next commit.
• Commit History: Saved snapshots of your work.
• Stash: Temporary store of changes.
• Remote: Central repo (like GitHub/GitLab).

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🚀 Basic Git Workflow

Step 1: Initialize & Setup Branches

git init
git branch br1
git branch br2
git checkout br1

Step 2: Work on br1

echo "Hello from br1" > file.txt
git add file.txt
git commit -m "br1: first commit"
# Repeat commit steps 3x

Step 3: Work on br2

git checkout br2
echo "Hello from br2" > file.txt
git add file.txt
git commit -m "br2: first commit"
# Repeat commit steps 3x

Step 4: Merge Branch to Main

git checkout main
git merge br1

Step 5: Cherry-pick Specific Commit

git cherry-pick <commit-hash>

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🔁 Advanced Commands

Rebase

git rebase main
# Makes commit history linear

Revert (safe for public branches)

git revert <commit-hash>

Reset (dangerous, modifies history)

git reset --soft HEAD~1   # Keep staged
git reset --mixed HEAD~1  # Keep unstaged
git reset --hard HEAD~1   # Discard all

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🌐 Remote Repos

Set up Remote

git remote add origin git@github.com-account1:username/repo.git
git push -u origin main

View Logs

git log --all --oneline

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🔑 SSH-Based Git Setup (Multi-Account)

Step 1: Generate SSH Keys

ssh-keygen -t rsa -b 4096 -C "email@example.com" -f ~/.ssh/id_rsa_account1

Repeat for each GitHub/GitLab account.

Step 2: Start SSH Agent

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_rsa_account1

Step 3: Configure SSH

Edit ~/.ssh/config:

# GitHub Account 1
Host github.com-account1
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa_account1
  IdentitiesOnly yes

# GitLab Account 2
Host gitlab.com-account2
  HostName gitlab.com
  User git
  IdentityFile ~/.ssh/id_rsa_account2
  IdentitiesOnly yes

💡 Don’t forget:

chmod 600 ~/.ssh/config

Step 4: Clone Using Custom Host

git clone git@github.com-account1:username/repo.git
git clone git@gitlab.com-account2:username/repo.git

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📤 Push Local Repo to Remote

git init
git add .
git commit -m "Initial commit"
git remote add origin git@github.com-account1:username/repo.git
git push -u origin main

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✅ Git Hooks

🔍 Pre-commit Hook: Block System.out.println

1. Create the hook:

touch .git/hooks/pre-commit
chmod +x .git/hooks/pre-commit

2. Script content:

#!/bin/bash

echo "🔍 Running pre-commit checks..."

files=$(git diff --cached --name-only --diff-filter=ACM | grep '\.java$')

for file in $files; do
  if grep -q "System.out.println" "$file"; then
    echo "🚫 Error: 'System.out.println' found in $file"
    exit 1
  fi
done

echo "✅ Pre-commit checks passed."
exit 0

🔒 Additional Pre-commit Validations

a. Block TODO/FIXME

grep -rnw 'src/' -e 'TODO\|FIXME' && echo "Remove TODOs before commit!" && exit 1

b. Prevent Large Files (>5MB)

find . -size +5M | grep -q . && echo "Too large files found!" && exit 1

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📜 Commit-msg Hook: Enforce Format

1. Create .git/hooks/commit-msg

touch .git/hooks/commit-msg
chmod +x .git/hooks/commit-msg

2. Add script:

#!/bin/bash

pattern="^(feat|fix|docs|style|refactor|test|chore)\([a-z]+\): .{10,}$"
if ! grep -qE "$pattern" "$1"; then
  echo "❌ Commit message format is invalid!"
  exit 1
fi

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🛠 Miscellaneous

• Set default branch to main:

git config --global init.defaultBranch main

• Checkout existing branch:

git checkout br1

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📂 Sample Repositories Cloned Using SSH

git clone git@github.com-account1:shariful-w3/microservices-config.git
git clone git@gitlab.com-account2:shaarifulz/portableportal.git

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🔗 Set Remote Repository Using SSH Config

Step 3: Add or update remote repo using your SSH configurations:

git remote set-url origin git@github.com-account1:shariful-w3/DevOps1Jenkins.git

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📌 Notes

• Always check .ssh/config if clone fails.
• Avoid System.out.println in production code.
• Use hooks to enforce standards.
• Prefer SSH for secure and multi-account Git access.

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🔧 Additional Useful Commands

✅ Install Java (OpenJDK 17)

To install Java on a Debian/Ubuntu-based system:

sudo apt update
sudo apt install openjdk-17-jdk

🚀 Running a Spring Boot Application with External Configuration

java -jar cismiddleware-0.0.1-SNAPSHOT.jar --spring.config.location=file:/root/cis-backend/executables/conf/

🔐 SSL Certificate Management with Let's Encrypt and PKCS12

Navigate to your certificate directory:

cd /etc/letsencrypt/live/example.com/

Backup the existing .p12 certificate:

mv springboot.p12 springboot.p12_old

Generate a new PKCS#12 (.p12) file from PEM certificates:

openssl pkcs12 -export -in fullchain.pem -inkey privkey.pem -out springboot.p12 -name springboot -CAfile chain.pem -caname root