🐚 ZENITH OS Shell

A Linux Bash-inspired interactive shell built from scratch in x86 Assembly Language — simulating how real operating systems handle commands at the hardware level.

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📸 Preview

Shell Startup

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🔄 Program Flow

💡 About The Project

ZENITH OS Shell is a DOS-based command-line shell developed as part of the Computer Organization & Assembly Language course

The goal was simple — build something that works like a real shell, but without any high-level language helping you. No frameworks, no libraries, no abstractions. Just registers, memory, and interrupts.

The shell mimics the look and feel of a Linux Bash terminal — complete with a pritam@root:$ prompt — and supports real filesystem operations like creating files, deleting them, navigating directories, and listing contents.

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⚙️ Supported Commands

Command	Description
ls	List contents of current directory
cd <dir>	Change directory
mkdir <name>	Create a new directory
create <file>	Create a new file
write <file>	Write text into a file
rm <file>	Delete a file
echo <text>	Print text to the screen
clear	Clear the screen
help	Display all available commands
about	Info about the developer
exit	Exit the shell

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🛠️ How To Run

Prerequisites

• DOSBox — DOS emulator
• MASM — Microsoft Macro Assembler

Steps

1. Clone the repository

git clone https://github.com/Pritam-Kumar-911/zenith-os-shell.git
cd zenith-os-shell

2. Assemble the source file

masm shell.asm;
link shell.obj;

3. Open DOSBox and mount the project folder

mount c <path-to-project-folder>
c:

4. Run the executable

shell.exe

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🏗️ How It Works

The shell runs as a continuous loop:

Start
  └── Print Banner
        └── Print Prompt (pritam@root:$)
              └── Read Input
                    └── Parse & Match Command
                          └── Execute → Repeat

Every command is matched manually using a custom string comparison routine. There are no built-in string functions — each character is compared byte by byte using CPU registers.

Filesystem operations like create, rm, mkdir, and cd are handled through DOS interrupt INT 21h — the same way real operating systems talk to hardware.

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📚 What I Learned

• How an OS shell actually processes and dispatches user commands
• Manual memory management — buffers, segments, and pointers
• How filesystem operations work at the system call level
• Low-level input/output using DOS interrupts
• Writing structured, maintainable code in Assembly without any abstractions

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👨‍💻 Developer

Pritam Kumar
CS Undergraduate — SZABIST, Karachi (Batch 2028)
GitHub

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Built as part of Computer Organization & Assembly Language course