nimbie-flash 0.0.3.dev13

Rust shell parser/interpreter bindings for Nimbie

Flash Shell

A POSIX-compliant shell parser, formatter, and interpreter implemented in Rust.

Flash is a high-performance, extensible toolkit for processing POSIX-style shell scripts. The system comprises three primary components: a lexical analyzer, a syntax parser, and an execution interpreter, all implemented from the ground up in Rust. Flash provides comprehensive support for real-world shell syntax and offers structured Abstract Syntax Tree (AST) access for static analysis, code transformation, and tooling development.

The project draws inspiration from mvdan/sh while prioritizing performance optimization and architectural extensibility through modern systems programming practices.

Development Status: This project is currently under active development and should be considered experimental for production use cases.

Table of Contents

• Feature Coverage
• Shell Implementation
• Library Integration

Feature Coverage

The following table provides a comprehensive overview of POSIX Shell and Bash feature support within the Flash implementation. This matrix serves as both a development roadmap and compatibility reference.

Legend:

• Fully Supported: Complete implementation with full functionality
• Parser Only: Syntax recognition and AST generation without execution support
• Not Supported: Feature not currently implemented

Category	Functionality / Feature	POSIX Shell	Bash	Flash	Implementation Notes
Basic Syntax	Variable assignment	Fully Supported	Fully Supported	Fully Supported	VAR=value syntax
	Command substitution	Fully Supported	Fully Supported	Fully Supported	Both $(cmd) and `cmd` forms
	Arithmetic substitution	Not Supported	Fully Supported	Fully Supported	$((expr)) evaluation
	Comments (#)	Fully Supported	Fully Supported	Fully Supported	Standard comment syntax
	Quoting (', "", \)	Fully Supported	Fully Supported	Fully Supported	All quoting mechanisms
	Globbing (*, ?, [...])	Fully Supported	Fully Supported	Fully Supported	Pattern matching
Control Structures	if / else / elif	Fully Supported	Fully Supported	Fully Supported	Conditional execution
	case / esac	Fully Supported	Fully Supported	Fully Supported	Pattern matching constructs
	for loops	Fully Supported	Fully Supported	Fully Supported	Iteration constructs
	while, until loops	Fully Supported	Fully Supported	Fully Supported	Loop constructs
	select loop	Not Supported	Fully Supported	Fully Supported	Interactive selection
	[[ ... ]] test command	Not Supported	Fully Supported	Fully Supported	Extended test expressions
Functions	Function definition (name() {})	Fully Supported	Fully Supported	Fully Supported	Standard function syntax
	function keyword	Not Supported	Fully Supported	Fully Supported	Bash-specific syntax
I/O Redirection	Output/input redirection (>, <, >>)	Fully Supported	Fully Supported	Fully Supported	Standard redirection
	Here documents (<<, <<-)	Fully Supported	Fully Supported	Parser Only	Partial implementation
	Here strings (<<<)	Not Supported	Fully Supported	Parser Only	Partial implementation
	File descriptor duplication (>&, <&)	Fully Supported	Fully Supported	Parser Only	Partial implementation
Job Control	Background execution (&)	Fully Supported	Fully Supported	Fully Supported	Process backgrounding
	Job control commands (fg, bg, jobs)	Fully Supported	Fully Supported	Fully Supported	Interactive mode only
	Process substitution (<(...), >(...))	Not Supported	Fully Supported	Parser Only	Basic <(cmd) support
Arrays	Indexed arrays	Not Supported	Fully Supported	Fully Supported	arr=(a b c) syntax
	Associative arrays	Not Supported	Fully Supported	Not Supported	declare -A requirement
Parameter Expansion	${var} basic expansion	Fully Supported	Fully Supported	Fully Supported	Variable expansion framework
	${var:-default}, ${var:=default}	Fully Supported	Fully Supported	Fully Supported	Default value expansion
	${#var}, ${var#pattern}	Fully Supported	Fully Supported	Fully Supported	Length and pattern operations
	${!var} indirect expansion	Not Supported	Fully Supported	Fully Supported	Variable indirection
	${var[@]} / ${var[*]} array expansion	Not Supported	Fully Supported	Not Supported	Array element expansion
Command Execution	Pipelines	Fully Supported	Fully Supported	Fully Supported	Command chaining
	Logical AND / OR (&&, `		`)	Fully Supported	Fully Supported
	Grouping (( ), { })	Fully Supported	Fully Supported	Fully Supported	Command grouping
	Subshell (( ))	Fully Supported	Fully Supported	Fully Supported	Isolated execution context
	Coprocesses (coproc)	Not Supported	Fully Supported	Not Supported	Bidirectional pipes
Builtins	cd, echo, test, read, eval, etc.	Fully Supported	Fully Supported	Fully Supported	Core built-in commands
	shopt, declare, typeset	Not Supported	Fully Supported	Not Supported	Bash-specific builtins
	let, local, export	Fully Supported	Fully Supported	Fully Supported	Variable management
Debugging	set -x, set -e, trap	Fully Supported	Fully Supported	Parser Only	Partial debugging support
	BASH_SOURCE, FUNCNAME arrays	Not Supported	Fully Supported	Not Supported	Runtime introspection
Miscellaneous	Brace expansion ({1..5})	Not Supported	Fully Supported	Fully Supported	Sequence generation
	Extended globbing (extglob)	Not Supported	Fully Supported	Not Supported	Requires shopt configuration
	Version variables ($BASH_VERSION)	Not Supported	Fully Supported	Fully Supported	$FLASH_VERSION in Flash
	Script sourcing (. or source)	Fully Supported	Fully Supported	Fully Supported	External script inclusion

Shell Implementation

Theoretical Foundation

A shell fundamentally operates as a macro processor that executes commands, where macro processing refers to the expansion of text and symbols into more complex expressions. The Unix shell paradigm encompasses dual functionality: serving as both a command interpreter and a programming language environment.

As a command interpreter, the shell provides the primary user interface to the comprehensive suite of Unix utilities and system commands. The programming language capabilities enable the composition and combination of these utilities into more sophisticated operations. Shell scripts, containing sequences of commands, achieve the same execution status as system binaries located in standard directories such as /bin, enabling users and organizations to establish customized automation environments.

Shell execution operates in two primary modes: interactive and non-interactive. Interactive mode processes user input from keyboard interfaces in real-time, while non-interactive mode executes command sequences from script files.

Flash maintains substantial compatibility with both POSIX shell (sh) and Bash specifications, implementing the core language features and execution semantics expected by existing shell scripts.

Production Readiness: Flash is currently in active development and should be evaluated carefully before deployment in production environments.

Python Package

The Python bindings are published as nimbie_flash, and import nimbie_flash is the supported import path.

The wheel can bundle a static flash-stdio-executor under nimbie_flash/bin/, and importing nimbie_flash will automatically export FLASH_STDIO_EXECUTOR_BIN when that bundled binary is present.

Installation Methods

Method 1: Cargo Package Manager

cargo install flash

Method 2: Source Installation

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

Method 3: Manual Binary Installation

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

# Linux systems
sudo cp target/release/flash /bin/

# macOS/BSD systems
sudo cp target/release/flash /usr/local/bin/

# Verify installation
flash

System Integration

Default Shell Configuration

To configure Flash as the default system shell:

# Add Flash binary path to system shells registry
vim /etc/shells

# Linux systems
chsh -s /bin/flash

# macOS/BSD systems
chsh -s /usr/local/bin/flash

Configuration Management

Flash implements a configuration system through the .flashrc initialization file located in the user's home directory. This file executes during shell startup, enabling environment customization and initialization script execution.

Prompt Customization

The shell prompt can be customized through the PROMPT environment variable within the .flashrc configuration file:

# Minimal prompt configuration
export PROMPT="flash> "

# Directory-aware prompt
export PROMPT='flash:$PWD$ '

# Full context prompt with user and hostname
export PROMPT='$USER@$HOSTNAME:$PWD$ '

The PROMPT variable supports full variable expansion, allowing integration of any available environment variables into the prompt display.

Configuration Example

# Prompt configuration
export PROMPT='flash:$PWD$ '

# Standard environment variables
export EDITOR=vim
export PAGER=less

# Future alias support (planned feature)
# alias ll="ls -la"
# alias grep="grep --color=auto"

---

Library Integration

Flash provides comprehensive library functionality for integration into Rust applications, supporting multiple use cases including testing frameworks, shell script parsing, custom shell backend development, code formatting, and static analysis tooling.

A WebAssembly version with interactive documentation and examples is available at raphamorim.io/flash.

Interpreter Integration

The Flash interpreter can be embedded directly into Rust applications:

use flash::interpreter::Interpreter;
use std::io;

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

The run_interactive method utilizes Flash's default evaluation engine:

// Default interactive shell implementation
pub fn run_interactive(&mut self) -> io::Result<()> {
    let default_evaluator = DefaultEvaluator;
    self.run_interactive_with_evaluator(default_evaluator)
}

Custom Evaluation Engine

Flash supports custom evaluation logic through the Evaluator trait, enabling specialized shell behavior:

// Evaluation trait for custom implementations
pub trait Evaluator {
    fn evaluate(&mut self, node: &Node, interpreter: &mut Interpreter) -> Result<i32, io::Error>;
}

// Standard shell behavior implementation
pub struct DefaultEvaluator;

impl Evaluator for DefaultEvaluator {
    fn evaluate(&mut self, node: &Node, interpreter: &mut Interpreter) -> Result<i32, io::Error> {
        match node {
            Node::Command { name, args, redirects } => {
                self.evaluate_command(name, args, redirects, interpreter)
            }
            Node::Pipeline { commands } => {
                self.evaluate_pipeline(commands, interpreter)
            }
            Node::List { statements, operators } => {
                self.evaluate_list(statements, operators, interpreter)
            }
            Node::Assignment { name, value } => {
                self.evaluate_assignment(name, value, interpreter)
            }
            // Additional node types...
            _ => Err(io::Error::other("Unsupported node type")),
        }
    }
}

The DefaultEvaluator implements comprehensive shell semantics including built-in command handling, pipeline execution, variable assignment, and external command invocation with proper environment variable propagation and I/O redirection support.

Lexical Analysis

Flash provides direct access to its lexical analyzer for token-level processing:

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
        );
    }

    // Verify complete token consumption
    let final_token = lexer.next_token();
    assert_eq!(final_token.kind, TokenKind::EOF);
}

#[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);
}

Syntax Analysis

The parser component transforms token streams into structured Abstract Syntax Trees:

use flash::lexer::Lexer;
use flash::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"),
    }
}

Code Formatting

Flash includes a comprehensive formatter for shell script standardization:

// String-based formatting
assert_eq!(
    Formatter::format_str("       # This is a comment"),
    "# This is a comment"
);

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

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

References

• GNU Bash Manual
• ShellCheck Static Analysis Tool
• Bash AST Visualization

License

This project is licensed under the GPL-3.0 License. Copyright © Raphael Amorim.