VSH - A Simple Unix Shell

VSH (V Shell) is a lightweight, custom Unix shell implementation written in C. It provides basic shell functionality with a clean, colorized interface and supports both built-in commands and external program execution.

Features

• Interactive Command Line: Colorized prompt showing username, hostname, and current directory
• Built-in Commands: cd, help, exit, and history commands with full functionality
• External Program Execution: Run any system command or program with argument support
• I/O Redirection: Full support for input (<), output (>), and append (>>) redirection
• Pipe Support: Chain commands together using pipes (|) for powerful command composition
• Environment Variables: Access and use environment variables (e.g., $HOME, $PATH, $USER)
• Command History: Persistent command history stored in ~/.vsh_history with readline integration
• Signal Handling: Proper handling of SIGINT (Ctrl+C) to interrupt running processes
• Home Directory Support: Navigate using ~ shorthand for home directory expansion
• Memory Management: Robust allocation and cleanup of dynamic memory with error handling

Project Structure

vsh/
├── include/      
│   ├── builtins.h
│   ├── colors.h  
│   ├── executor.h
│   ├── parser.h  
│   ├── shell.h   
│   ├── signals.h 
│   └── utils.h   
├── src/          
│   ├── builtins.c
│   ├── executor.c
│   ├── main.c    
│   ├── parser.c  
│   ├── shell.c   
│   ├── signals.c 
│   └── utils.c   
├── obj/    
├── Makefile
└── vsh     

Installation

Prerequisites

• GCC compiler
• GNU Readline library
• POSIX-compliant Unix system (Linux, macOS, etc.)

Installing Dependencies

Ubuntu/Debian:

sudo apt-get install gcc libreadline-dev

CentOS/RHEL:

sudo yum install gcc readline-devel

Fedora:

sudo dnf install gcc readline-devel

macOS:

# Install Xcode command line tools
xcode-select --install
# Install Homebrew if not already installed
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
# Install readline
brew install readline

Arch Linux:

sudo pacman -S gcc readline

Building and Installing

git clone https://github.com/Vatsalj17/vsh.git
cd vsh
make
sudo make install

This will:

1. Build the vsh executable
2. Install it to /usr/local/bin/vsh (accessible system-wide)

Usage

Run the shell:

./vsh        # If built locally
# or
vsh          # If installed system-wide

You'll see a colorized prompt in the format:

username@hostname - current_directory took time status_code
⊱

Built-in Commands

• cd [directory]: Change directory (supports ~ for home directory)
• help: Display available commands and shell features
• exit: Exit the shell gracefully
• history: Display command history (stored in ~/.vsh_history)

External Commands and Advanced Features

Any system command or program can be executed with full support for advanced shell features:

Basic Commands:

ls -la
grep "pattern" file.txt
gcc -o program program.c
python script.py

I/O Redirection:

ls > file_list.txt          # Redirect output to file
cat < input.txt             # Redirect input from file
echo "text" >> log.txt      # Append output to file

Pipes:

ls -la | grep ".txt"        # List files and filter for .txt files
cat file.txt | sort | uniq  # Sort and remove duplicates
ps aux | grep "vsh"         # Find vsh processes

Environment Variables:

echo $HOME                  # Display home directory
echo $PATH                  # Display PATH variable
ls $HOME/Documents          # Use variables in commands

Signal Handling

• Ctrl+C (SIGINT): Interrupts the currently running command without exiting the shell
• Ctrl+D (EOF): Exits the shell gracefully

Code Organization

Core Components

1. Parser (parser.c): Tokenizes user input into command arguments
2. Executor (executor.c): Handles command execution (built-ins vs external programs)
3. Shell Interface (shell.c): Manages the interactive prompt and user input
4. Built-ins (builtins.c): Implements built-in shell commands
5. Utilities (utils.c): Helper functions for user info and path management
6. Signal Handling (signals.c): Manages signal handling for process control

Key Features Implementation

• Process Management: Uses fork() and execvp() for external command execution
• Path Resolution: Supports both absolute paths and home directory shortcuts
• Memory Safety: Proper allocation, deallocation, and error handling
• Color Support: ANSI color codes for enhanced visual experience

Cleaning Up

To remove VSH from your system:

sudo make uninstall

To clean build artifacts:

make clean

Known Limitations

• No background process support (&)
• No command substitution (`command` or $(command))
• No shell scripting support (if/while/for loops)
• Limited tab completion (relies on readline's default behavior)