Evolve mosh shell to be the default userland shell for meniOS

[pbalduino]

Goal

Evolve the basic shell implementation in app/mosh (meniOS shell) to become the default userland shell for meniOS with essential bash-like functionality.

Context

Currently, there's a very basic shell implementation in app/mosh that serves as a starting point. As meniOS progresses toward full userland support, we need a functional shell that users can interact with to launch programs, navigate the filesystem, and perform basic system operations.

Definition of Done

• Command parsing: Parse basic command lines with arguments
• Built-in commands: Implement essential built-ins (cd, ls, pwd, exit, help)
• Program execution: Launch userland programs via exec syscalls
• File operations: Basic file manipulation (cat, cp, mv, rm) when filesystem is available
• Environment: Basic environment variable support
• History: Simple command history functionality
• Tab completion: Basic filename/command completion (nice-to-have)
• Error handling: Proper error messages and graceful failure handling
• Prompt customization: Configurable prompt showing current directory

Implementation Details

• Build upon existing code in app/mosh/
• Keep implementation simple and lightweight for educational OS
• Focus on core functionality rather than advanced features
• Integrate with meniOS syscall interface
• Design for single-user, single-session usage initially

Built-in Commands to Implement

• cd [directory] - Change current directory
• ls [directory] - List directory contents
• pwd - Print working directory
• cat <file> - Display file contents
• echo <text> - Print text to console
• help - Show available commands
• exit - Exit shell
• clear - Clear screen

Dependencies

• Syscall interface (write, read, open, close, etc.)
• Filesystem support and VFS layer
• ELF loader for launching programs
• Process management for userland programs
• Basic userland C library functions

Integration Points

• Launch as default shell after kernel boot
• Integrate with userland process lifecycle
• Work with meniOS filesystem when implemented
• Provide platform for testing other userland applications

Future Enhancements

• Job control (background processes)
• Pipes and redirection
• Shell scripting capabilities
• More advanced built-ins
• Configuration files

Files to Work With

• app/mosh/ - Existing shell implementation
• Integration with userland build system
• Documentation for shell usage

Testing Strategy

• Test basic command parsing and execution
• Verify built-in commands work correctly
• Test error handling for invalid commands
• Validate integration with filesystem operations
• Ensure proper cleanup on exit

This shell will serve as the primary user interface for meniOS and provide a platform for testing other userland applications, including eventually launching Doom! 🎮