Linux Mini Shell

📌 Project Description

A lightweight, professional, POSIX-compliant UNIX CLI application written in C from scratch. This project demonstrates core operating system concepts such as process creation, inter-process communication (IPC), file descriptor manipulation, and robust signal handling. It closely mirrors the behavior of standard shells like bash or sh while remaining modular, highly documented, and extremely easy to install.

🎥 Demo

✨ Features

• Execution: Runs standard foreground and background (&) processes.
• Pipelining: Supports unlimited chained pipelines (e.g., ls -l | grep src | wc -l).
• I/O Redirection: Handles input (<), output (>), and append (>>) file redirection.
• Built-in Commands: cd, exit, and history.
• Signal Handling: Gracefully handles SIGINT (Ctrl+C) without crashing, and automatically reaps background zombie processes via SIGCHLD.
• CLI Options: Supports standard --help and --version flags.

🏗️ Architecture Overview

The shell is built with a clean, modular architecture separating concerns across dedicated C modules:

• shell.c: The main REPL (Read-Eval-Print Loop).
• parser.c: Parses raw string input into structured Command data objects.
• execute.c: Handles single-command fork() and execvp() logic.
• pipe.c: Orchestrates N-1 pipes for N commands, chaining standard I/O streams.
• redirect.c: Manages file opens and dup2() descriptor mapping.
• signals.c: Installs isolated signal handlers and manages state restoration for child processes.
• builtin.c & history.c: Implements internal commands and memory-managed command history.

📂 Folder Structure

linux-mini-shell/
├── Makefile
├── README.md
├── CHANGELOG.md
├── CONTRIBUTING.md
├── docs/
├── assets/
├── tests/
├── include/
└── src/

🛠️ System Calls Used

This project extensively utilizes UNIX system calls to interface directly with the kernel:

• Process Management: fork(), execvp(), waitpid()
• IPC & Pipes: pipe(), dup2()
• File I/O: open(), close(), read(), write()
• Signals: signal(), sigaction(), kill()
• Environment: chdir()

🚀 Build & Run

To build and run the project locally, ensure you have gcc and make installed.

# Clone the repository
git clone https://github.com/HarshEvolves/linux-mini-shell.git
cd linux-mini-shell

# Build the project
make

# Run the shell
./minishell

⚡ Quick Start

# Display help menu
./minishell --help

# Check version
./minishell --version

💡 Usage Examples

myshell$ pwd
/Users/harsh/linux-mini-shell

myshell$ ls
Makefile  README.md  src  include  tests  assets  docs

myshell$ echo Hello
Hello

myshell$ echo Hello > out.txt

myshell$ cat out.txt
Hello

myshell$ ls | grep main
main.c

🚀 Future Improvements

• Logical Operators: Support for && and ||.
• Job Control: Implementation of fg, bg, and jobs commands using SIGTSTP.
• Quoting & Escaping: Support for parsing strings containing spaces inside double/single quotes.
• Environment Variables: Support for expanding $VAR variables and export.

🤝 Contributing

Contributions are always welcome! Please see CONTRIBUTING.md for details on how to get started.

📄 License

This project is open-source. See the LICENSE file for details.