my-docs/Code-Management/Git/main.md

Git Commands Guide for DevOps Engineers

Professional Reference Document
Comprehensive Git workflow for development, CI/CD pipelines, and team collaboration

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Table of Contents

1. Installation and Setup
2. SSH Key Configuration
3. Repository Initialization
4. Basic Workflow
5. Status and History
6. File Operations
7. Branch Management
8. Merging and Rebasing
9. Remote Operations
10. Commit Management
11. Removing Commits
12. Stash Operations
13. Tags and Releases
14. .gitignore Management
15. Configuration and Aliases
16. Troubleshooting and Recovery
17. Repository Cloning

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1. Installation and Setup

Install Git

Download from official source: git-scm.com

Linux Distributions:

# Debian/Ubuntu
sudo apt update && sudo apt install git -y

# RHEL/CentOS/Fedora
sudo yum install git -y    # or dnf install git -y

macOS:

brew install git

Verify Installation

git --version

Displays installed Git version

Configure User Identity

Git requires author information for every commit:

git config --global user.name "Your Full Name"
git config --global user.email "your.email@company.com"

Configuration Scopes:

Scope	Command Flag	Applies To	Persistence
System	--system	All users on machine	System-wide
Global	--global	Current user	User account
Local	--local	Specific repository	Repository only

Verify Configuration:

git config --list

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2. SSH Key Configuration

Generate SSH Key Pair

ssh-keygen -t ed25519 -C "your.email@company.com"

• -t ed25519: Modern, secure key algorithm
• -C: Comment for key identification

SSH Agent Management

# Start SSH agent
eval "$(ssh-agent -s)"

# Add private key to agent
ssh-add ~/.ssh/id_ed25519

Per-Repository SSH Key

# Set custom key for specific repo
git config --local core.sshCommand "ssh -i /path/to/custom_key"

# Clone with specific key (one-time)
git -c core.sshCommand="ssh -i /path/to/key" clone git@host:repo.git

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3. Repository Initialization

Create New Repository

# Initialize with main branch
git init -b main

# Initialize with default branch
git init

Key Concepts:

• Working Directory: Files not yet tracked by Git
• Staging Area (Index): Files prepared for commit
• Repository: Committed history and metadata

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4. Basic Workflow

Stage Changes

# Stage all changes (new, modified, deleted)
git add -A

# Stage specific files
git add <file1> <file2>

# Stage all modified files (not new files)
git add .

Commit Changes

git commit -m "Descriptive commit message"

Connect to Remote

git remote add origin <repository-url>
git remote -v    # Verify remote configuration

Push to Remote

# First push (sets upstream tracking)
git push -u origin main

# Subsequent pushes
git push

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5. Status and History

Repository Status

git status

Shows working directory and staging area state

Commit History

# One-line summary
git log --oneline

# Visual graph of all branches
git log --graph --oneline --all

# Last N commits with patch
git log -p -3

# Show specific commit details
git show <commit-hash>

Change Visualization

# Unstaged changes (working directory)
git diff

# Staged changes (index vs HEAD)
git diff --staged

# Branch comparison
git diff main..develop

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6. File Operations

Operation	Command	Effect
Stage file	git add <file>	Moves file to staging area
Unstage	git reset <file>	Removes from staging, keeps changes
Discard changes	git restore <file>	Reverts to last committed version
Rename	git mv old new	Stages rename operation
Remove (tracked)	git rm <file>	Stages file deletion
Untrack	git rm --cached <file>	Removes from Git, keeps locally

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7. Branch Management

Branch Operations

# Create and switch
git switch -c feature/new-api

# List branches
git branch -v          # Local branches with last commit
git branch -a          # All branches (local + remote)

# Delete branch
git branch -d feature  # Safe delete (merged)
git branch -D feature  # Force delete

# Rename branch
git branch -m old-name new-name

Branch States:

• Local Branch: Exists only in your repository
• Remote Branch: Exists on remote server (origin/main)
• Tracking Branch: Local branch linked to remote (main -> origin/main)

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8. Merging and Rebasing

Merge (Preserves History)

git checkout main
git merge feature/xyz

Merge Types:

Type	Condition	Result
Fast-forward	Target ahead, no divergence	Linear history
Three-way	Both branches have new commits	Merge commit created

Rebase (Linear History)

git checkout feature/xyz
git rebase main

Rebase Controls:

git rebase --abort     # Cancel rebase
git rebase --continue  # Resolve conflicts and continue

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9. Remote Operations

Remote Management

git remote -v              # List remotes
git remote show origin     # Detailed remote info
git fetch --all            # Fetch all remotes

Pull Strategies

git pull                   # Fetch + merge
git pull --rebase          # Fetch + rebase (cleaner history)

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10. Commit Management

Modify Last Commit

git commit --amend         # Edit message/files

Safe Undo (Shared Branches)

git revert <commit-hash>   # Creates reversing commit

Reset Types

git reset --soft HEAD~1    # Keeps staging area
git reset HEAD~1           # Unstages, keeps files
git reset --hard HEAD~1    # Discards everything

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11. Removing Commits

Remove Local (Unpushed) Commit

# Soft reset (interactive rebase recommended)
git reset --soft HEAD~1

# Interactive rebase for multiple commits
git rebase -i HEAD~3
# Change 'pick' to 'drop' or delete line

Remove Pushed Commit from Remote

⚠️ DANGER: Rewrites shared history

# 1. Reset locally
git reset --hard HEAD~1

# 2. Force push (collaborators must coordinate)
git push --force-with-lease origin main

# 3. Alternative: Safer revert
git revert HEAD    # Creates undoing commit
git push

Team Coordination Required:

1. Notify team before force push
2. Team runs: git fetch && git reset --hard origin/main
3. Use revert for shared production branches

Remove Specific Pushed Commit

# Interactive rebase
git rebase -i <commit-before-target>~1

# Or create revert
git revert <specific-commit-hash>

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12. Stash Operations

Temporary Storage:

git stash push -m "WIP: API changes"
git stash list
git stash apply stash@{0}    # Keep stash
git stash pop                # Apply and remove

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13. Tags and Releases

Tag Management

# Lightweight tag
git tag v1.2.3

# Annotated tag (recommended)
git tag -a v1.2.3 -m "Release v1.2.3"

# Push tags
git push origin --tags

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14. .gitignore Management

Create/Update:

touch .gitignore

Common Patterns:

# Dependencies
node_modules/
vendor/

# Logs
*.log
logs/

# Environment
.env
*.env.local

# OS
.DS_Store
Thumbs.db

Apply Existing .gitignore:

git rm -r --cached .
git add . && git commit -m "Apply .gitignore"

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15. Configuration and Aliases

Editor and Pager

git config --global core.editor "code --wait"

Productivity Aliases

git config --global alias.st "status"
git config --global alias.co "checkout"
git config --global alias.br "branch -v"
git config --global alias.cm "!f() { git add -A && git commit -m \"$@\"; }; f"

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16. Troubleshooting and Recovery

Common Recovery

# View all history (including resets)
git reflog

# Recover deleted branch
git checkout -b recovery-branch <commit-hash>

# Fix detached HEAD
git checkout main

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17. Repository Cloning

# Standard clone
git clone <url>

# Specific branch
git clone -b develop <url>

# Shallow clone (history limited)
git clone --depth 1 <url>

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Key Git Concepts Explained

Concept	Definition	Importance
HEAD	Current commit/branch pointer	Always points to active commit
Index/Staging	Intermediate area between working dir and repo	Prepares exact commit content
Fast-forward	Linear merge without merge commit	Clean history
Detached HEAD	HEAD points directly to commit	Use for inspection, create branch to save work
Reflog	Local history of HEAD movements	Recovery lifeline
Force Push	Overwrites remote history	Use only with team coordination

Document Version: 2.0
Optimized for DevOps workflows, CI/CD integration, and team collaboration