C-Shell — Modular Unix-like Shell in C

A custom Unix-like shell built in C, supporting command execution, foreground/background process handling, piping, redirection, shell logging, and modular built-in utilities.

Overview

This project implements a lightweight Unix-like shell from scratch with a focus on:

• command parsing and execution
• foreground and background process handling
• piping and I/O redirection
• shell prompt rendering
• persistent command logging
• custom built-in commands
• shell customization through rc-style configuration

The shell is organized modularly so that parsing, execution, prompting, logging, and built-ins are separated across source files.

Features

Core Shell Features

• interactive shell prompt
• execution of standard Unix commands
• foreground and background process support
• signal-aware shell behavior
• modular command dispatch architecture

I/O Features

• command parsing and tokenization
• piping support
• input redirection (<)
• output overwrite redirection (>)
• output append redirection (>>)

Built-in Utilities

• seek — file and directory search utility
• proclore — process inspection utility
• neonate — monitoring utility
• iman — custom manual/help command
• shell logging support
• shell rc configuration via myshrc

Project Structure

.
├── Makefile
├── readme.md
└── src
    ├── main.c
    ├── prompt.c / prompt.h
    ├── inputhandler.c / inputhandler.h
    ├── commandhandler.c / commandhandler.h
    ├── color.c / color.h
    ├── log.c / log.h
    ├── proclore.c / proclore.h
    ├── seek.c / seek.h
    ├── myshrc.c / myshrc.h
    ├── neonate.c / neonate.h
    └── iman.c / iman.h

Prerequisites

You need:

• gcc
• make
• libcurl development package

Ubuntu / Debian

sudo apt update
sudo apt install build-essential libcurl4-openssl-dev

Fedora

sudo dnf install gcc make libcurl-devel

Arch Linux

sudo pacman -S base-devel curl

Build Instructions

Clone the repository:

git clone https://github.com/garimamittal13/C-shell.git
cd C-shell

Build the shell:

make

This creates the executable:

./my_shell

How to Run the Shell

After building the project, start the shell by running:

./my_shell

You should now see the custom shell prompt and can start typing commands.

Example Session

./my_shell
pwd
ls
echo hello

Running Commands in Background

sleep 10 &

Using Pipes

ls | wc
cat file.txt | grep hello

Using Redirection

echo hello > out.txt
sort < input.txt
cat file.txt >> log.txt

Using Built-in Commands

seek filename
proclore
neonate
iman seek

Cleaning Build Files

To remove object files and the compiled executable:

make clean

Design Highlights

• Modular architecture: parsing, execution, prompting, logging, and built-ins are implemented as separate modules.
• Extensible built-ins: custom shell commands are isolated cleanly, making the shell easier to extend.
• Systems programming focus: emphasizes process handling, pipes, redirection, and shell control flow in C.

Learning Outcomes

Through this project, I explored:

• Unix process creation and execution
• shell command parsing
• pipes and file descriptor redirection
• modular systems programming in C
• implementation of custom shell utilities
• integrating external libraries like libcurl

Tech Stack

• Language: C
• Build System: Makefile
• Concepts: operating systems, processes, pipes, redirection, shell design, modular programming

Future Improvements

Potential extensions include:

• command history navigation
• tab completion
• improved job control
• aliases and environment variable expansion
• more built-in shell utilities