🐚 microbash: A Custom Unix Shell

A lightweight, custom Unix shell implemented entirely in C. This project is a hands-on exploration of Operating System principles, designed to parse and execute commands just like standard shells (e.g., bash, zsh), while managing processes, file descriptors, and inter-process communication under the hood.

✨ Key Features

• Command Execution: Runs standard Unix system commands using the exec family of system calls.
• Built-in Commands: Native support for essential shell commands like cd (change directory) and exit.
• I/O Redirection: Supports redirecting standard input (<) and standard output (>) to files.
• Piping (|): Connects the standard output of one command to the standard input of another, allowing command chaining.
• Background Processes (&): Executes commands in the background without blocking the shell prompt.

📂 Project Structure

• microbash.c: The core source code containing the shell loop, string parsing logic, and system call invocations.
• Makefile: The build configuration file for easy compilation.
• microbash.pdf: Detailed project specification and architectural documentation.
• test.txt: A sample text file used to verify I/O redirection and piping functionalities.

🛠️ Technologies & Concepts

• Language: C
• API: POSIX (Portable Operating System Interface)
• Process Management: fork(), execvp(), waitpid()
• Inter-Process Communication (IPC): pipe()
• File Operations: open(), close(), dup2()

🚀 How to Build and Run

1. Open your terminal in the project directory.
2. Compile the shell using the provided Makefile:

   make

3. Run the compiled executable to start the shell interface:

   ./microbash

(To exit the shell, simply type exit or press Ctrl+D)

🧠 What I Learned

Building a shell from the ground up is a classic and rigorous exercise in Systems Programming. Through microbash, I developed a deep understanding of:

• Process Lifecycle: How the OS creates child processes (fork), replaces their memory images (exec), and synchronizes with the parent (wait).
• File Descriptors: How Unix treats files and I/O streams, and how to safely manipulate them using dup2 to achieve redirection.
• Inter-Process Communication: Creating anonymous pipes to establish one-way data channels between concurrent processes.
• C String Manipulation: Safely tokenizing user input, handling dynamic memory, and dealing with pointers in a low-level environment.