SimpleShell

Overview

SimpleShell is a lightweight, custom-built Unix shell implemented in C. It supports command execution, piped commands, directory navigation, and a persistent command history stored in shared memory.

Features

• Basic Command Execution: Supports execution of standard Linux commands.
• Piping: Allows execution of multiple commands connected by pipes (|).
• Built-in Commands:
  • cd (Change directory)
  • mkdir (Create directories)
  • history (Display command history)
• Command History Tracking:
  • Stores executed commands along with process ID and execution time.
  • Uses shared memory (shm_open, mmap) to maintain history across processes.
• Signal Handling:
  • Captures Ctrl+C (SIGINT) to display command history before exit.
• Concurrency Management:
  • Uses semaphores for safe concurrent access to shared memory.

Compilation & Execution

Prerequisites

Ensure you have GCC installed:

sudo apt update && sudo apt install gcc

Compile

gcc simpleshell.c -o simpleshell -lrt -pthread

Run the Shell

./simpleshell

Usage

Upon running, the shell displays a custom prompt:

meechan@UNI:/current/directory$

Running Commands

Execute standard Linux commands, e.g.:

ls -l
echo "Hello, World!"

Using Piped Commands

Commands can be connected via pipes:

ls -l | grep .c | wc -l

Built-in Commands

• Change Directory

  cd /path/to/directory

• Create Directory

  mkdir new_folder

• View Command History

  history

Exiting

Press Ctrl+C to display history and exit safely.

Implementation Details

• Shared Memory (shm_open, mmap): Stores history information persistently.
• Semaphores (sem_t): Ensures safe concurrent access to shared memory.
• Process Management (fork, execvp, wait): Handles command execution and pipelining.
• Signal Handling (signal(SIGINT, handler)): Captures Ctrl+C and ensures graceful exit.

Future Enhancements

• Add support for background processes (& operator).
• Implement output redirection (> and <).
• Enhance error handling for unsupported commands.

License

This project is open-source and licensed under the MIT License.