Build Your Own Shell

This project is a custom implementation of a POSIX-compliant shell built in JavaScript. It supports executing external commands, built-in commands, and features like tab completion, command parsing, and redirection.

Features

• Built-in Commands:

  • cd: Change the current working directory.
  • pwd: Print the current working directory.
  • echo: Print arguments to standard output.
  • exit: Exit the shell.
  • type: Display information about a command (e.g., whether it's built-in or external).

• External Commands:

  • Executes programs available in the system's PATH.

• Tab Completion:

  • Autocompletes built-in commands and external executables.
  • Handles cases where multiple matches exist, completing to the longest common prefix or displaying all matches.

• Redirection:

  • Supports output redirection (>, >>) and error redirection (2>, 2>>).

• Error Handling:

  • Gracefully handles invalid commands and displays appropriate error messages.

Getting Started

Prerequisites

• Node.js: Ensure you have Node.js (version 21 or higher) installed on your system.

Installation

1. Clone the repository:

   git clone https://github.com/your-username/build-your-own-shell.git
   cd build-your-own-shell

2. Install dependencies

   npm install

Running the Shell

To start the shell, run:

./your_program.sh

You will see a prompt ($ ) where you can enter commands.

Usage

Built-in Commands

• cd : Change the current working directory.

$ cd /path/to/directory

• pwd: Print the current working directory.

$ pwd

• echo : Print text to standard output.

$ echo Hello, World!

• exit: Exit the shell.

$ exit

• type : Display information about a command.

$ type echo
echo is a shell builtin

External Commands

You can run any executable available in your system's PATH. For example: $ ls -l $ node --version

Tab Completion

Press to autocomplete commands or filenames. If multiple matches exist, press twice to display all matches.

Redirection

• Redirect standard output to a file: $ echo "Hello" > output.txt

• Append to a file: $ echo "World" >> output.txt

• Redirect standard error: $ ls nonexistentfile 2> error.log

• Append standard error: $ ls nonexistentfile 2>> error.log

Development

Project Structure

• app/main.js: Entry point for the shell.
• app/InputHandler.js: Handles user input and tab completion.
• app/OutputHandler.js: Handles output and redirection.
• app/CommandRegistry.js: Manages built-in and external commands.
• app/<CommandName>.js: Implementations of built-in commands (e.g., CdCommand, PwdCommand).

Adding a New Built-in Command

• Create a new file in the app directory (e.g., MyCommand.js).
• Extend the Command class and implement the execute method.
• Register the command in main.js: