MiniShell++

A lightweight Unix-like shell developed in C++ using POSIX system calls. MiniShell++ demonstrates core operating system concepts including process creation, command execution, pipelines, I/O redirection, background job management, signal handling, and modular shell architecture.

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📑 Table of Contents

• ✨ Features
• 🛠️ Technologies
• 📁 Project Structure
• ⚙️ POSIX System Calls Used
• 🚀 Build Instructions
• 💻 Usage
• 📝 Built-in Commands
• 📋 Sample Session
• ⚠️ Current Limitations
• 🚀 Future Improvements
• 📸 Screenshots
• 🎯 Learning Outcomes
• 👨‍💻 Author
• 📄 License

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✨ Features

• Built-in Commands (cd, history, exit)
• External Command Execution
• Single-stage Pipelines (|)
• Input Redirection (<)
• Output Redirection (>)
• Append Redirection (>>)
• Background Job Execution (&)
• Signal Handling (SIGINT, SIGCHLD)
• Command History
• Filename Completion Engine (complete <prefix>)
• Modular C++ Architecture
• CMake Build System

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🛠️ Technologies

• C++17
• POSIX System Calls
• Linux / macOS
• CMake

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📁 Project Structure

MiniShell++
│
├── assets/
│   ├── shell-demo.png
│   ├── pipeline.png
│   ├── redirection.png
│   ├── background-job.png
│   └── history.png
│
├── include/
│   ├── autocomplete.h
│   ├── builtin.h
│   ├── command.h
│   ├── executor.h
│   ├── history.h
│   ├── parser.h
│   ├── pipeline.h
│   ├── process.h
│   ├── shell.h
│   └── signal_handler.h
│
├── src/
│   ├── autocomplete.cpp
│   ├── builtin.cpp
│   ├── command.cpp
│   ├── executor.cpp
│   ├── history.cpp
│   ├── main.cpp
│   ├── parser.cpp
│   ├── process.cpp
│   ├── shell.cpp
│   └── signal_handler.cpp
│
├── tests/
├── assets/
├── build/
├── CMakeLists.txt
├── README.md
└── .gitignore

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⚙️ POSIX System Calls Used

MiniShell++ is built using core POSIX APIs.

System Call	Purpose
fork()	Create child processes
execvp()	Execute external commands
waitpid()	Wait for child processes
pipe()	Inter-process communication
dup2()	Redirect standard input/output
open()	Open files for redirection
close()	Close file descriptors
sigaction()	Install signal handlers

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🚀 Build Instructions

Clone Repository

git clone https://github.com/Balpreet1003/MiniShell++.git

cd MiniShell++

Build

mkdir build

cd build

cmake ..

make

Run

./myshell

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💻 Usage

External Commands

pwd

ls -la

mkdir demo

whoami

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Pipeline

echo hello | wc

ls | wc

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Input / Output Redirection

echo hello > out.txt

echo world >> out.txt

cat < out.txt

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Background Jobs

sleep 10 &

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File Completion

complete out

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📝 Built-in Commands

Command	Description
cd	Change current directory
history	Display command history
exit	Exit MiniShell

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📋 Sample Session

myshell> pwd
/Users/balpreet_singh/Documents/MiniShell++

myshell> ls
build
include
src
README.md
CMakeLists.txt

myshell> echo hello > out.txt

myshell> cat out.txt
hello

myshell> echo world >> out.txt

myshell> cat out.txt
hello
world

myshell> ls | wc
       7       7      76

myshell> sleep 10 &
[12345] Running in background

myshell> history
1 pwd
2 ls
3 echo hello > out.txt
4 cat out.txt
5 sleep 10 &
6 history

myshell> exit

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⚠️ Current Limitations

This project intentionally focuses on implementing the core functionality of a Unix shell.

Currently, the following features are not supported:

• Multiple pipelines (cmd1 | cmd2 | cmd3)
• Combined pipeline and redirection
• Environment variable expansion ($PATH)
• Wildcard expansion (*)
• Quote parsing
• Command aliases
• Interactive Tab completion (uses complete <prefix>)

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🚀 Future Improvements

Potential future enhancements include:

• Multiple pipeline support
• Environment variable expansion
• Wildcard expansion
• Quote parsing
• Interactive Tab completion using termios or GNU Readline
• Job control (jobs, fg, bg)
• Persistent command history
• Colored shell prompt

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📸 Screenshots

1. Shell Startup

Launch the shell and execute standard Unix commands.

./myshell

pwd

ls

whoami

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2. Pipeline Execution

echo hello | wc

ls | wc

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3. Input / Output Redirection

echo hello > out.txt

echo world >> out.txt

cat out.txt

cat < out.txt

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4. Background Job Execution

sleep 10 &

pwd

history

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5. Command History

history

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🎯 Learning Outcomes

Through this project, I gained practical experience with:

• Unix Shell Design
• Operating System Fundamentals
• POSIX System Calls
• Process Management
• Inter-Process Communication
• File Descriptor Manipulation
• Signal Handling
• Modular C++ Software Design
• CMake Build System

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👨‍💻 Author

Balpreet Singh Gill

• GitHub: https://github.com/Balpreet1003
• LinkedIn: https://www.linkedin.com/in/balpreet-singh-gill-72374925b/

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📄 License

This project is developed for educational and learning purposes.