Custom Unix Shell (wsh)

Overview

wsh is a custom Unix shell that replicates and extends the functionality of traditional Unix/Linux shells. It was developed as part of the CS 537: Introduction to Operating Systems course at the University of Wisconsin–Madison. This project provides hands-on experience with process management, inter-process communication, and system-level programming.

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Key Features

• Command Execution: Run standard Unix/Linux commands and scripts seamlessly.
• Command History: Store and reuse previously executed commands for enhanced usability.
• Environment Variables: Manage local variables with a custom-built hashmap.
• I/O Redirection: Support for input/output redirection and piping between processes.
• Batch Scripting: Execute .wsh script files for task automation.

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Purpose

This project was designed to:

• Deepen understanding of operating system concepts through practical implementation.
• Master system calls like fork(), execvp(), and pipe().
• Improve resource utilization techniques and process management.
• Enhance skills in C programming and Unix/Linux system programming.

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Technical Implementation

Command History

The shell uses a circular array to manage command history efficiently, storing a fixed number of commands and discarding the oldest as new commands are added.

Environment Variables

Environment variables are handled using a hashmap with chaining to resolve collisions, enabling quick and efficient storage and retrieval of local variables.

Piping and I/O Redirection

The pipe() system call is used for inter-process communication. More advanced execution scenarios are supported through redirection of standard input (stdin) and output (stdout) using dup2().

Process Management

Core system calls like fork() and execvp() are utilized for process creation and execution, ensuring concurrent process handling and efficient resource usage.

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Getting Started

Prerequisites

• Operating System: Unix/Linux
• Compiler: GCC or any compatible C compiler

Installation

1. Clone the repository:

   git clone git@github.com:SrujayReddy/Custom-Unix-Shell.git cd Custom-Unix-Shell

2. Compile the code:

   gcc wsh.c -o wsh

3. Run the shell:

   ./wsh

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Usage

Basic Commands

Run standard Unix/Linux commands:

ls -l
pwd

Piping

Redirect the output of one command as input to another:

ls | grep ".c"

Input/Output Redirection

Redirect input and output to/from files:

cat < input.txt > output.txt

Command History

Access previously executed commands:

history

Batch Scripting

Write commands in a .wsh script file:

echo "Hello, World!"
mkdir new_project
cd new_project

Run the script:

./wsh script.wsh

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Challenges & Learning

This project helped me:

• Master system-level programming concepts like process creation, signals, and inter-process communication.
• Implement complex functionalities such as piping and I/O redirection efficiently.
• Debug and optimize resource management and edge-case handling in a concurrent environment.

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Future Enhancements

• Add support for job control features (fg, bg, jobs).
• Enhance scripting with loops and conditionals.
• Introduce customizable shell prompts and aliasing.

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License

This project was developed as part of the CS 537: Introduction to Operating Systems course at the University of Wisconsin–Madison. It is shared strictly for educational and learning purposes only.

Important Notes:

• Redistribution or reuse of this code for academic submissions is prohibited and may violate academic integrity policies.
• The project is licensed under the MIT License. Any usage outside academic purposes must include proper attribution.