JShell - Modern Unix Shell Implementation

A feature-rich Unix shell written in C that provides an interactive command-line interface with advanced features like command history, file completion, job control, and alias management.

✨ Features

Core Functionality

• Command execution with argument handling
• Input/Output redirection (>, >>, <)
• Pipeline support (|)
• Background process execution (&)
• Environment variable management
• Job control (foreground/background processes)
• Alias management with name validation
• Command history with search
• Subshell support using ( ... ) for grouping commands
• Logical operators (&&, ||)
• Support for control structures (if, while, for, case)

Interactive Features

• Command history navigation (Up/Down arrows)
• Cursor movement (Left/Right arrows)
• Tab completion for commands and files
• Color-coded prompt and output
• Directory-aware path completion
• Intelligent command suggestions
• Error detection and reporting

Scripting Features

• Shell script support with .jsh extension
• Environment variable expansion in scripts
• Command pipelines and redirection
• Background process management
• Error reporting with line numbers
• Comment support with #
• Full access to built-in commands
• Custom startup configuration via .jshellrc

Built-in Commands

Command	Description
help	Display help message
cd [dir]	Change directory
exit	Exit the shell
env	Show environment variables
export VAR=value	Set environment variable
unset VAR	Remove environment variable
alias name='cmd'	Create or show aliases
unalias name	Remove an alias
jobs	List background jobs
history	Lists all commands used
history [n]	Displays last n commands
fg [%job]	Bring job to foreground
bg [%job]	Continue job in background
kill %job	Terminate specified job

🌟 Advanced Features

Alias Management

• Create and manage command aliases
• Protection against recursive aliases
• Strict name validation (letters, numbers, underscore)
• Support for aliases in pipelines
• Quote handling in alias values

Job Control

• Background process management
• Job suspension (Ctrl+Z) and resumption
• Foreground/Background job switching
• Job status monitoring
• Process group management
• Signal handling (e.g., SIGINT, SIGTSTP)

Input/Output Features

• Command history persistence
• Intelligent tab completion
• Directory-aware path completion
• Input line editing
• Signal handling (Ctrl+C, Ctrl+Z)
• Proper terminal control

🚀 Getting Started

Prerequisites

• GCC compiler
• Make build system
• Unix-like operating system (Linux/macOS)

Installation

1. Clone the repository:

   git clone https://github.com/jalenfran/shell.git
   cd shell

2. Build the project:

   make

Running the Shell

There are several ways to use JShell:

1. Direct command (after installation):

   jshell

2. Development version:

   ./bin/jshell

3. Running Scripts:

   # Method 1: Using jshell command
   jshell script.jsh
   
   # Method 2: Make script executable
   chmod +x script.jsh
   ./script.jsh

Example Script (example.jsh)

# Print a welcome message
echo "Welcome to JShell!"

# List all files in the current directory
ls -la

# Create an alias for `ls`
alias ll='ls -l'

# Change directory to /tmp
cd /tmp

# Print environment variables
env

📁 Project Structure

shell/  
├── scripts/                # Directory for shell scripts
│   └── jshell-wrapper      # Wrapper script for JShell
├── src/                    # Source code files  
│   ├── alias.c             # Alias management implementation
│   ├── alias.h             # Alias management declarations
│   ├── builtin_commands.c  # Built-in commands implementation
│   ├── builtin_commands.h  # Built-in commands declarations
│   ├── builtin_commands_impl.c  # Implementation of built-in commands
│   ├── command.h           # Command structure and functions
│   ├── command_registry.c  # Command registry implementation
│   ├── command_registry.h  # Command registry declarations
│   ├── constants.h         # Shell constants and configurations
│   ├── executor.c          # Command execution logic
│   ├── history.c           # History management
│   ├── history.h           # History function declarations
│   ├── input.c             # Input handling and completion
│   ├── job_manager.c       # Job management implementation
│   ├── job_manager.h       # Job management declarations
│   ├── jobs_signals.c      # Signal handling for jobs
│   ├── main.c              # Shell initialization and main loop
│   ├── parser.c            # Command parsing and tokenization
│   ├── rc.c                # Configuration file handling
│   ├── rc.h                # Configuration file declarations
│   ├── shell.h             # Main shell header
├── bin/                    # Binary output directory  
│   └── jshell              # Compiled executable (generated)
├── obj/                    # Object files directory (generated)
│   ├── alias.o  
│   ├── builtin_commands.o  
│   ├── command_registry.o  
│   ├── executor.o  
│   ├── history.o  
│   ├── input.o  
│   ├── job_manager.o  
│   ├── jobs_signals.o  
│   ├── main.o  
│   ├── parser.o  
│   ├── rc.o  
├── .gitignore              # Git ignore file
├── .jshellrc               # JShell configuration file
├── LICENSE                 # License file (MIT)
├── Makefile                # Build configuration

📜 License

This project is licensed under the MIT License. See the LICENSE file for more details.

🤝 Contributing

Contributions are welcome! Feel free to submit issues, feature requests, or pull requests to improve JShell.

📞 Support

If you encounter any issues, check the GitHub Issues page or reach out to the maintainers.

Enjoy using JShell! 🚀