Rash - Bidirectional Shell Safety Tool

Bidirectional shell safety tool that purifies legacy bash scripts and lets you write shell scripts in REAL Rust with automatic safety guarantees.

Table of Contents

• What's New
• Why Rash?
• Quick Start
• Features
• Core Commands
• Advanced Testing
• Documentation
• Quality Metrics
• Shell Compatibility
• Performance
• MCP Server
• Contributing
• License

🚀 What's New in v6.46.0

Latest Release - 2025-12-21

• Probar Integration: Three new CLI commands for advanced testing
  • bashrs playbook - State machine testing for shell scripts
  • bashrs mutate - Mutation testing with 10 mutation operators
  • bashrs simulate - Deterministic simulation replay with seed control
• Transpiler Bug Hunt: 130-point Popper Falsification Checklist (T001-T130)
• Dockerfile Linting: 30-point D-code validation (D001-D030)
• Test Suite: 7,445 tests passing (100% pass rate)
• PMAT Score: 133/134 (Grade A+)

See CHANGELOG.md for complete release notes.

Why Rash?

Shell scripts are everywhere—CI/CD pipelines, deployment automation, system configuration—but they're notoriously difficult to write safely. Rash solves this by providing:

1. Bidirectional Safety: Write in Rust and transpile to shell, or purify existing bash scripts
2. Automatic Transformation: Don't just detect problems—fix them automatically
3. Deterministic Guarantees: Same input always produces identical, reproducible output
4. Zero Runtime Dependencies: Generated scripts run on any POSIX-compliant system

Features

• 🛡️ Automatic Safety: Protection against shell injection, word splitting, glob expansion
• 🔍 Beyond Linting: Full AST semantic understanding - transforms code, doesn't just warn
• 📦 Zero Runtime Dependencies: Generated scripts work on any POSIX shell
• 🎯 Deterministic Output: Same input always produces identical scripts
• ✅ ShellCheck Compliant: All output passes strict linting

How Rash Exceeds ShellCheck

What ShellCheck Does	What Rash Does
⚠️ Warns: "$RANDOM is non-deterministic"	✅ Rewrites to version-based deterministic IDs
⚠️ Warns: "mkdir may fail if exists"	✅ Transforms to mkdir -p (idempotent)
⚠️ Warns: "Unquoted variable expansion"	✅ Quotes all variables automatically
Static pattern matching	Full AST semantic understanding
Detects issues (read-only)	Fixes issues (read-write transformation)

Key Difference: ShellCheck tells you what's wrong. Rash understands your code's intent and rewrites it to be safe, deterministic, and idempotent — automatically.

Quick Start

Installation

# From crates.io (recommended)
cargo install bashrs

# Or from source
git clone https://github.com/paiml/bashrs
cd bashrs
cargo install --path rash

Write Rust, Get Safe Shell

// install.rs
#[rash::main]
fn main() {
    let version = env_var_or("VERSION", "1.0.0");
    let prefix = env_var_or("PREFIX", "/usr/local");

    echo("Installing MyApp {version} to {prefix}");

    mkdir_p("{prefix}/bin");
    mkdir_p("{prefix}/share/myapp");

    if exec("cp myapp {prefix}/bin/") {
        echo("✓ Binary installed");
    } else {
        eprint("✗ Failed to install binary");
        exit(1);
    }
}

Transpile to safe POSIX shell:

$ bashrs build install.rs -o install.sh

Or Purify Existing Bash

Before (messy bash):

#!/bin/bash
SESSION_ID=$RANDOM                      # Non-deterministic
mkdir /app/releases/$RELEASE            # Non-idempotent
rm /app/current                         # Fails if doesn't exist

After (purified by Rash):

#!/bin/sh
session_id="session-${version}"         # ✅ Deterministic
mkdir -p "/app/releases/${release}"     # ✅ Idempotent
rm -f "/app/current"                    # ✅ Safe removal

Core Commands

# Transpile Rust to shell
bashrs build input.rs -o output.sh

# Purify legacy bash scripts
bashrs purify messy.sh -o clean.sh

# Interactive REPL with debugging
bashrs repl

# Lint shell scripts (including Dockerfiles)
bashrs lint script.sh

# Test bash scripts
bashrs test script.sh

# Quality scoring
bashrs score script.sh

# Comprehensive audit
bashrs audit script.sh

Advanced Testing

Rash includes Probar integration for comprehensive quality assurance:

# State machine testing with playbooks
bashrs playbook install.playbook.yaml --run

# Mutation testing (goal: >90% kill rate)
bashrs mutate script.sh --count 10

# Deterministic simulation replay
bashrs simulate script.sh --seed 42 --verify

Mutation Operators: Rash applies 10 mutation operators including string mutations, command substitutions, conditional inversions, and redirect modifications to verify test quality.

📚 Documentation

The Rash Book is the canonical source for all documentation:

→ Read The Rash Book

Quick links:

• Getting Started
• Quick Start Tutorial
• Linting Rules
• Configuration Management
• API Reference

Why the book?

• ✅ All examples automatically tested
• ✅ Always up-to-date with latest release
• ✅ Comprehensive coverage of all features
• ✅ Real-world examples and tutorials

Quality Metrics

Metric	Value	Status
PMAT Score	133/134 (99.3%)	✅ Grade A+
Tests	7,445 passing	✅ 100% pass rate
Coverage	91.22%	✅ Exceeds 85% target
T-code Falsification	142/142	✅ 130-point checklist
D-code Falsification	31/31	✅ Dockerfile validation
ShellCheck	100% compliant	✅ All output passes
Shell Compatibility	6 shells	✅ sh, dash, bash, ash, zsh, mksh

Falsification Testing (Popper Methodology)

Rash uses Popperian falsification—tests attempt to disprove functionality rather than prove it works:

# Run 130-point transpiler falsification checklist
cargo test -p bashrs --test transpiler_tcode_tests

# Run 30-point Dockerfile falsification checklist
cargo test -p bashrs --test dockerfile_dcode_tests

A passing test means the falsification attempt failed—the feature works correctly.

Shell Compatibility

Generated scripts are tested on:

Shell	Version	Status
POSIX sh	-	✅ Full support
dash	0.5.11+	✅ Full support
bash	3.2+	✅ Full support
ash (BusyBox)	1.30+	✅ Full support
zsh	5.0+	✅ Full support
mksh	R59+	✅ Full support

Performance

Rash is designed for fast transpilation:

• Rust-to-Shell: 21.1µs transpile time
• Makefile Parsing: 0.034-1.43ms (70-320x faster than targets)
• Memory Usage: <10MB for most scripts

MCP Server

Rash provides a Model Context Protocol (MCP) server for AI-assisted shell script generation:

# Install MCP server
cargo install rash-mcp

# Run server
rash-mcp

Available in the official MCP registry as io.github.paiml/rash.

Contributing

We welcome contributions! See our Contributing Guide for details.

# Clone and test
git clone https://github.com/paiml/bashrs.git
cd bashrs
make test

# Run all quality checks
make validate

License

MIT License. See LICENSE for details.

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For comprehensive documentation, visit The Rash Book