C-Shell: A Custom UNIX Command-Line Interpreter in C

A lightweight, portable UNIX shell built from scratch in C, demonstrating core concepts of operating systems including process management, system calls, and memory handling.

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About The Project

This project is a fully functional command-line interpreter that mimics the core behavior of shells like bash or zsh. It was developed to apply and deepen understanding of low-level systems programming. The shell can parse user input, execute system commands, and handle built-in functions, making it a robust example of C programming in a systems context.

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Technical Skills Showcase

This project demonstrates proficiency in:

• C Programming: Implemented using modern, clean C (C11 standard) with a focus on memory safety and portability.
• Operating Systems Concepts:
  • Process Management: Utilizes fork() and execvp() to create and manage child processes for command execution.
  • System Calls: Interacts directly with the kernel using calls like chdir(), waitpid(), and signal() for core functionality.
  • Signal Handling: Implements custom handlers for SIGINT (Ctrl-C) to ensure shell stability.
• Memory Management: Employs dynamic memory allocation (malloc, realloc, free) for efficient handling of commands and arguments of any length.
• Software Design: Structured with a modular, multi-file architecture (parser, executor, shell core) and documented with Doxygen for maintainability.

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Features

• Command Execution: Runs any command located in the system's $PATH.
• Built-in Commands:
  • cd: Changes the current directory.
  • exit: Terminates the shell.
• Robust I/O: Reads user input of any length using getline().
• Dynamic Argument Handling: Parses command lines with a variable number of arguments.

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Installation & Usage

Prerequisites

• A C compiler (e.g., GCC)
• A UNIX-like environment (Linux, macOS)

Build Instructions

1. Clone the repository:

   git clone https://github.com/your-username/your-repo-name.git
   cd your-repo-name

2. Compile the source code:

   gcc -Wall -Wextra -std=c11 -o my_shell main.c shell.c parser.c execute.c

Running the Shell

1. Execute the compiled program:

   ./my_shell

2. Start using the shell:

   x > ls -l
   x > pwd
   x > exit

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Project Structure

The project is organized into logical modules for clarity and separation of concerns:

• main.c: Entry point of the program.
• shell.c / shell.h: Core REPL (Read-Eval-Print Loop) and signal handling.
• parser.c / parser.h: Functions for tokenizing user input into commands and arguments.
• execute.c / execute.h: Logic for executing built-in and external commands.