mystsh

Mystical shell parser, formatter, and interpreter with Bash support

This library provides a fast and extensible parser, formatter, and interpreter for POSIX-style shell scripts, written entirely in Rust. Inspired by mvdan/sh, but built from the ground up for performance, correctness, and hackability.

It understands real-world shell code, handles edge cases, and offers structured access to ASTs for tooling, analysis, or code transformation.

✨ Features

• ✅ Robust parser producing an abstract syntax tree (AST)
• ✅ Pretty-printer/formatter with customizable indentation
• ✅ Interpreter for executing shell scripts
• ✅ Interactive REPL mode
• ✅ Friendly, safe Rust API

🚀 Example: Parse, Format, Execute

use std::env;
use std::error::Error;

fn main() -> Result<(), Box<dyn Error>> {
    println!("Shell Parser, Formatter, and Interpreter Demo");

    demo_parser()?;
    demo_formatter()?;
    demo_interpreter()?;

    if env::args().any(|arg| arg == "--interactive") {
        let mut interpreter = Interpreter::new();
        interpreter.run_interactive()?;
    }

    Ok(())
}

🔍 Parsing

#!/bin/bash
echo "Hello, world!"
for i in $(seq 1 10); do
  echo "Count: $i"
done

The parser turns this into a typed AST structure:

List:
  Command: echo ["Hello, world!"]
  Operator: ;
  ForLoop: i in $(seq 1 10)
    Command: echo ["Count: $i"]

🎨 Formatting

Messy shell script?

if [ $x -eq 42 ]; then echo "The answer"; elif [ $x -lt 42 ]; then echo "Too low"; else echo "Too high"; fi

Formatted with consistent indentation:

if [ $x -eq 42 ]; then
  echo "The answer"
elif [ $x -lt 42 ]; then
  echo "Too low"
else
  echo "Too high"
fi

🧪 Interpreting

Run shell scripts programmatically (including variable handling, I/O, and exit codes):

MESSAGE="Hello from the interpreter"
echo $MESSAGE

Output: Hello from the interpreter Exit code: 0

💻 Interactive Mode

Launch an interactive shell with:

cargo run -- --interactive
$ echo hello
hello
$ exit

🔧 API

let ast = parse_script(script)?;
let formatted = format_script(script, "  ");
let result = Interpreter::new().execute(script)?;

🦀 Why Rust?

• Memory safety without GC
• Lightning-fast tooling
• Easy integration into other Rust projects
• Great for embedding in editors or dev tools

📦 Installation

cargo install mystsh

📚 License

MIT or Apache 2.0 — your choice.