myst (work in progress)

A mystical shell parser, formatter, and interpreter written in Rust.

Myst is a fast, extensible, and hackable toolkit for working with POSIX-style shell scripts. It includes a parser, formatter, and interpreter built from scratch in Rust. Myst understands real-world shell syntax and provides structured AST access for static analysis, tooling, and transformation.

Inspired by mvdan/sh, but engineered from the ground up with performance and extensibility in mind.

Motivation

Myst was created to serve two main purposes: as a learning project to better understand shell parsing and syntax, and as a tool for testing and embedding within the Rio terminal emulator, a GPU-accelerated terminal written in Rust.

Install as your shell

⚠️ Myst is still under development. Use it with caution in production environments.

git clone https://github.com/raphamorim/myst.git
cd myst
cargo build --release

# MacOS/BSD: Change /bin/ to /usr/local/bin/
sudo cp target/release/myst /bin/
myst

🔌 Embed in Your Rust Project

As an Interpreter

use mystsh::interpreter::Interpreter;
use std::io;

fn main() -> io::Result<()> {
    let mut interpreter = Interpreter::new();
    interpreter.run_interactive()?;
    Ok(())
}

As a Lexer/Tokenizer

fn test_tokens(input: &str, expected_tokens: Vec<TokenKind>) {
    let mut lexer = Lexer::new(input);
    for expected in expected_tokens {
        let token = lexer.next_token();
        assert_eq!(
            token.kind, expected,
            "Expected {:?} but got {:?} for input: {}",
            expected, token.kind, input
        );
    }

    // Ensure we've consumed all tokens
    let final_token = lexer.next_token();
    assert_eq!(
        final_token.kind,
        TokenKind::EOF,
        "Expected EOF but got {:?}",
        final_token.kind
    );
}

#[test]
fn test_function_declaration() {
    let input = "function greet() { echo hello; }";
    let expected = vec![
        TokenKind::Function,
        TokenKind::Word("greet".to_string()),
        TokenKind::LParen,
        TokenKind::RParen,
        TokenKind::LBrace,
        TokenKind::Word("echo".to_string()),
        TokenKind::Word("hello".to_string()),
        TokenKind::Semicolon,
        TokenKind::RBrace,
    ];
    test_tokens(input, expected);
}

As a Parser

use mystsh::lexer::Lexer;
use mystsh::parser::Parser;

#[test]
fn test_simple_command() {
    let input = "echo hello world";
    let lexer = Lexer::new(input);
    let mut parser = Parser::new(lexer);
    let result = parser.parse_script();

    match result {
        Node::List {
            statements,
            operators,
        } => {
            assert_eq!(statements.len(), 1);
            assert_eq!(operators.len(), 0);

            match &statements[0] {
                Node::Command {
                    name,
                    args,
                    redirects,
                } => {
                    assert_eq!(name, "echo");
                    assert_eq!(args, &["hello", "world"]);
                    assert_eq!(redirects.len(), 0);
                }
                _ => panic!("Expected Command node"),
            }
        }
        _ => panic!("Expected List node"),
    }
}

Myst Feature Coverage

This table outlines the supported features of POSIX Shell and Bash. Use it to track what your Myst parser and interpreter implementation in Rust supports.

Legends:

• ✅ fully supported.
• ⚠️ only supported in parser and formatter.
• ❌ not supported.

📦 Crate Info

Add Myst to your Cargo.toml:

mystsh = "0.x"

TODO

• If for parser and interop.
• Functions for parser and interop.
• Loops for parser and interop.
• Array for parser and interop.
• Control + w.

License

GPL-3.0 License © Raphael Amorim