hsh

A Unix shell written in Haskell.

Why?

Well, a few reasons:

1. Because I can.
2. Shells exercise most of the capabilities a production-ready language needs, from I/O to process management to file and directory operations to string parsing to state management. About the only thing shells don't do much of is network I/O.
3. It's accessible. My first Haskell project was an OpenSSH-compatible SFTP server which is somewhat obscure.

Overview

Features

• Single-command parser
• Support for env vars through setenv and getenv
• Settable prompts
• Ability to cd and run external commands
• $PATH is consulted for command lookups; it automatically updates when $PATH changes or a directory on the path is changed.

Misfeatures

• Mis-invoking builtins (like setenv foo when the correct invocation is setenv foo bar) causes the shell to treat setenv as an external command.

Non-Features

This is a programming exercise focused on an interactive command interpreter. I haven't much interest right now in building support for Bourne-style scriptability.

To-Do List

1. (DONE) Basic command-line interpreter.
   1. (DONE) Shell-ish parser
   2. (DONE) ENV var support
   3. (DONE) Trivial prompt generator
   4. (DONE) Fundamental builtins
      1. cd
2. (DONE) Command Look-Up Table creation from $PATH
3. (DONE and removed since it's no longer needed) rehash builtin
4. (DONE) Smart rehash based on $PATH changes and mtimes of each dir named in $PATH
5. (DONE) Stop crashing on command ENOENTs.
6. (DONE) Shell variable substitution
7. Output redirection
8. Command-name tab completion
9. Argument tab completion
10. Programmable prompts