slash: Unix Shell Implementation

Operating Systems - Project 1
Spring 2025 | Koç University

Contributors

• Sinemis Toktaş
• Yamaç Ömür

Overview

This repository showcases Project 1 from the Operating Systems course completed at Koç University during Spring 2025. slash is a comprehensive Unix-style shell implemented in C, featuring advanced I/O operations, kernel module integration, and modern shell conveniences.

Key Features

Core Functionality

• Custom Path Resolution: Manual PATH searching without execp() functions
• I/O Redirection: Support for >, >>, and < operators
• Piping: Arbitrary-length command chains with | operator
• Shell Scripting: Execute .sh files line by line

Advanced Features

• Auto-completion: Tab completion for executables in PATH directories
• Command History: Navigate 140 previous commands with arrow keys
• Beautiful Prompt: Rich interface showing user, hostname, and directory
• Built-in Commands: exit, cd, history, and custom lsfd

Kernel Module Integration

• Custom lsfd Command: Analyze file descriptors for any process
• Dual Implementation: User-space fallback + kernel module via /proc/lsfd
• Automatic Management: Load module on startup, cleanup on exit
• Advanced Output: FD number, filename, size, and full path

Usage

Basic Commands

# Interactive mode
./shell-skeleton

# Script execution
./shell-skeleton script.sh

# Example session
ˢˡᵃsh ╰┈➤ ls -la | grep txt > files.out
ˢˡᵃsh ╰┈➤ lsfd 1234 fd_info.txt
ˢˡᵃsh ╰┈➤ history

Build & Run

# Build shell
gcc -o shell-skeleton shell-skeleton.c

# Build kernel module
cd module/
make

# Run
./shell-skeleton

Technical Features

• Process Management: Sophisticated fork/exec handling for pipe chains
• Memory Safety: Proper allocation/deallocation in user and kernel space
• Terminal Control: Raw input handling for history and auto-completion
• Kernel Programming: Safe navigation of kernel data structures with RCU locking

Learning Outcomes

This project demonstrates proficiency in:

• System Programming: Advanced Unix system calls and process management
• Kernel Development: Loadable kernel modules and /proc filesystem
• Operating System Concepts: Practical implementation of OS principles
• Memory Management: Dynamic allocation in both user and kernel space