🚀 C Shell

A powerful Unix shell implementation with modern features

Experience the power of a custom shell with advanced features like piping, I/O redirection, and background processes

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🤔 What is a Shell?

A shell is a command-line interpreter that provides a user interface for accessing an operating system's services. Think of it as the bridge between you and your computer's core functions.

🖥️ Shell vs Terminal vs Command Prompt

Shell Type	Platform	Description
🐧 Bash	Linux/macOS	Most popular Unix shell
🐚 Zsh	Linux/macOS	Enhanced shell with modern features
🔵 PowerShell	Windows	Microsoft's advanced shell
⚫ CMD	Windows	Traditional Windows command prompt
🚀 Our C Shell	Unix/Linux	Custom implementation with modern features

💡 Why Build a Custom Shell?

• 🎓 Learn how operating systems work internally
• 🔧 Understand process management and system calls
• 🚀 Customize your command-line experience
• 💪 Master low-level programming concepts

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✨ Features

🎯 Core Functionality ⚡ Fast command execution 🔄 Interactive shell loop 📁 Dynamic directory display 🛡️ Signal handling (Ctrl+C) 🧹 Automatic process cleanup

🔧 Advanced Features 🔀 Piping - Chain commands (|) 📤 I/O Redirection - <, >, >> 🔙 Background Jobs - Run with & 💻 Built-in Commands - cd, help, exit 🎨 Colored Prompt - Shows current directory

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🚀 Quick Start

Prerequisites

⚠️ Platform Requirements:

• Unix-like Operating System (Linux, macOS, BSD)
• Or Windows with WSL (Windows Subsystem for Linux)
• Not compatible with native Windows

📦 Build Requirements:

# Ensure you have GCC installed
gcc --version

# On Ubuntu/Debian
sudo apt install build-essential

# On macOS
xcode-select --install

# On Windows - Install WSL first
wsl --install

🔨 Compilation

git clone https://github.com/Het-2004/Build-your-own-shell.git
cd Build-your-own-shell
gcc -o advanced_shell advanced_shell.c

🎮 Run the Shell

./advanced_shell

You'll see the beautiful prompt:

🚀 /current/working/directory > 

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📖 Usage Guide

🏠 Basic Commands

# List files
🚀 ~/projects > ls -la

# Show current directory
🚀 ~/projects > pwd

# Echo text
🚀 ~/projects > echo "Hello, Advanced Shell!"

🔧 Built-in Commands

Command	Description	Example
cd	Change directory	cd /home/user/Documents
help	Show help menu	help
exit	Exit the shell	exit

🔀 Piping Magic

# Find all C files
🚀 ~/project > ls -la | grep "\.c$"

# Count lines in files
🚀 ~/project > cat *.txt | wc -l

# Search and sort
🚀 ~/project > grep "function" *.c | sort

📁 I/O Redirection

# Save output to file
🚀 ~/project > ls -la > file_list.txt

# Append to file
🚀 ~/project > echo "New entry" >> file_list.txt

# Read from file
🚀 ~/project > wc -l < large_file.txt

# Combine both
🚀 ~/project > sort < input.txt > sorted_output.txt

🔙 Background Processing

# Run long process in background
🚀 ~/project > sleep 60 &
Started background job with PID: 12345

# Continue using shell immediately
🚀 ~/project > ls
🚀 ~/project > echo "Shell is still responsive!"

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🏗️ Architecture

graph TD
    A[User Input] --> B[Shell Loop]
    B --> C{Parse Command}
    C --> D[Built-in Command?]
    D -->|Yes| E[Execute Built-in]
    D -->|No| F[Fork Process]
    F --> G{Redirection?}
    G -->|Yes| H[Setup I/O]
    G -->|No| I[Execute Command]
    H --> I
    I --> J{Pipe?}
    J -->|Yes| K[Create Pipe]
    J -->|No| L[Wait/Background]
    K --> L
    L --> B
    E --> B

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🧩 Core Components

• 🔄 Shell Loop: Main interactive loop handling user input
• ⚙️ Command Parser: Tokenizes and processes command strings
• 🚀 Process Manager: Handles fork/exec for external commands
• 🔀 Pipe Handler: Manages inter-process communication
• 📁 I/O Manager: Handles file redirection operations
• 🛡️ Signal Handler: Manages system signals gracefully

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🎯 Advanced Examples

🔥 Power User Commands

# Complex pipeline with redirection
🚀 ~/logs > cat access.log | grep "ERROR" | sort | uniq -c > error_summary.txt

# Background compilation
🚀 ~/project > make all > build.log 2>&1 &

# Multi-step data processing
🚀 ~/data > cat raw_data.csv | cut -d',' -f2 | sort -n | tail -10

🧪 Testing Your Shell

# Test I/O redirection
echo "test content" > test.txt
cat < test.txt
cat test.txt | wc -l

# Test background processes
sleep 5 &
ps aux | grep sleep

# Test piping
ls -la | head -5 | tail -3

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🔍 Technical Deep Dive

🛠️ Implementation Highlights

📋 Process Management

• Uses fork() for creating child processes
• execvp() for command execution with PATH resolution
• waitpid() for proper process synchronization
• Zombie process prevention with SIGCHLD handling

🔀 Pipe Implementation

• Creates anonymous pipes with pipe()
• Proper file descriptor duplication with dup2()
• Handles both read and write ends correctly
• Supports single-pipe commands (extensible to multiple)

📁 I/O Redirection

• File descriptor manipulation for stdin/stdout
• Support for input (<), output (>), and append (>>)
• Proper file opening with appropriate flags
• Error handling for file operations

📊 Performance Characteristics

Feature	Performance	Memory Usage
Command Parsing	O(n)	Fixed buffers
Process Creation	Fork overhead	Minimal
I/O Redirection	File I/O speed	Low overhead
Pipe Operations	Kernel buffered	Efficient

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🎨 Customization

🎯 Modify the Prompt

Edit the prompt in shell_loop():

printf("🚀 %s > ", cwd);  // Current prompt
printf("⭐ %s $ ", cwd);  // Alternative style
printf("[%s] → ", cwd);   // Minimal style

🔧 Add Built-in Commands

1. Add function declaration
2. Implement the function
3. Add to builtin_str[] array
4. Add to builtin_func[] array

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🐛 Troubleshooting

Common Issues

❌ Compilation Errors

# Missing headers
sudo apt-get install libc6-dev

# GCC not found
sudo apt-get install gcc

# Permission denied
chmod +x advanced_shell

🔧 Runtime Issues

• Command not found: Check PATH variable
• Permission denied: Verify file permissions
• Segmentation fault: Check command length limits
• Zombie processes: Built-in SIGCHLD handling

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🤝 Contributing

We welcome contributions! Here's how to get started:

🌟 How to Contribute

1. 🍴 Fork the repository
2. 🌿 Create a feature branch (git checkout -b feature/amazing-feature)
3. ✨ Commit your changes (git commit -m 'Add amazing feature')
4. 📤 Push to the branch (git push origin feature/amazing-feature)
5. 🔄 Open a Pull Request

🎯 Areas for Contribution

• 🔄 Multiple pipe support
• 📚 Command history
• ⌨️ Tab completion
• 🌐 Environment variables
• 📜 Script execution
• 🎮 Job control commands

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🛣️ Roadmap

🚀 Upcoming Features

• 🔄 Multiple Pipes - Support cmd1 | cmd2 | cmd3
• 📚 Command History - Arrow key navigation
• ⌨️ Tab Completion - Auto-complete commands and files
• 🌐 Variables - Environment variable expansion
• 📜 Scripting - Execute shell scripts
• 🎮 Job Control - jobs, fg, bg commands
• 🔗 Aliases - Custom command shortcuts
• ⚙️ Config Files - .shellrc support

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📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

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🙏 Acknowledgments

Special thanks to:

• 🔧 Unix Philosophy - Simple, composable tools
• 📚 POSIX Standards - Cross-platform compatibility
• 🎓 Educational Goals - Understanding OS concepts
• 🌟 Open Source Community - Inspiration and support

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