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.

Option 1:

cargo install mystsh

Option 2:

git clone https://github.com/raphamorim/myst.git
cd myst && cargo install --path .

Option 3:

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

Interpreter readline support

• ✅ Kill Ring: Text deleted with Ctrl+K, Ctrl+U, or Ctrl+W is saved to a kill ring, allowing it to be yanked (pasted) with Ctrl+Y.
• ✅ Ability to transpose characters with Ctrl+T.
• ✅ Incremental History Search: Pressing Ctrl+R initiates a search through command history. Pressing Ctrl+R again searches for the next occurrence of the same pattern.
• ✅ Bidirectional character and word movement keys.
• ✅ Ctrl+A: Move cursor to the beginning of the line.
• ✅ Ctrl+E: Move cursor to the end of the line.
• ✅ Ctrl+B: Move backward one character (same as left arrow).
• ✅ Ctrl+F: Move forward one character (same as right arrow).
• ✅ Ctrl+K: Cut text from cursor to end of line (kill).
• ✅ Ctrl+U: Cut text from beginning of line to cursor (kill).
• ✅ Ctrl+Y: Paste (yank) previously killed text.
• ✅ Ctrl+P: Previous history entry (same as up arrow).
• ✅ Ctrl+N: Next history entry (same as down arrow).
• ✅ Ctrl+T: Transpose (swap) characters at cursor.
• ✅ Ctrl+D: Delete character under cursor (or exit if line is empty).
• ✅ Ctrl+R: Reverse incremental search through history.
• ✅ Ctrl+W: Delete word backward.
• ✅ Ctrl+L: Clear screen and redraw prompt.
• ✅ Ctrl+C: Cancel/interrupt.
• ✅ Arrow keys for navigation and history.

🔌 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"),
    }
}

As Formatter

assert_eq!(
    Formatter::format_str("       # This is a comment"),
    "# This is a comment"
);

Or by receiving AST

let mut formatter = Formatter::new();
let node = Node::Comment(" This is a comment".to_string());

assert_eq!(formatter.format(&node), "# This is a comment");

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

• Remove interop custom functions from run_interop and allow to receive as parameter. It will split the current code there to bin.rs file.
• Functions for parser and interop.
• Loops for parser and interop.
• Array for parser and interop.

Resources

• https://www.gnu.org/software/bash/manual/bash.html
• https://www.shellcheck.net/
• https://stackblitz.com/edit/bash-ast?file=src%2Fapp%2Fapp.component.ts

License

GPL-3.0 License © Raphael Amorim