🐀 rat: Next-Gen CLI File Viewer

💡 Why rat?

rat is a powerful, feature-rich command-line utility that goes beyond simple file viewing. It combines streaming simplicity with modern enhancements including SSH support, archive viewing, structured data rendering, Git annotations, and inline image display.

⭐ Key Features

• TTY-aware dual mode - raw byte-perfect output when piped, rich mode when attached to a terminal

• SSH Support - view files on remote servers seamlessly

• Extended Language Support - 15+ programming languages with custom configuration support

• Archive Viewing - .gz, .bz2, .tar, .zip and more

• Structured Data Viewers - JSON tree visualization, CSV tables

• Git Annotations - inline git blame with author and date information

• Inline Image Display - supports Kitty, iTerm2, w3m, and Sixel protocols

• Plugin Architecture - JSON-RPC based plugin system for custom renderers

• Type Safe - built with Crystal for compile-time type safety

• Input/Output Sanitization - safe handling of binary and malformed data

• Paging Control - --paging=auto|always|never for external pager integration

• Line-range & Limit Options - --lines=START-END, --max-lines=N

• Clean Codebase in Crystal v1.18.2 - fast binary, easy to build & distribute

• Input/Output Sanitization - safe handling of binary and malformed data

• Paging Control - --paging=auto|always|never for external pager integration

• Line-range & Limit Options - --lines=START-END, --max-lines=N

• Clean Codebase in Crystal v1.18.2 - fast binary, easy to build & distribute

🚀 Quick Start

Install

# Clone and build
git clone https://github.com/OkaVatti/rat.git
cd rat
shards install
crystal build main.cr -o rat --release

Usage

# Basic file viewing with syntax highlighting
./rat file.cr

# SSH file viewing
./rat -S -L user@192.168.1.100:22 -K ~/.ssh/id_rsa -l "/home/user/code.rs"

# View with line numbers
./rat -n main.cr

# Git blame annotations
./rat -g lib/rat/cli.cr

# View JSON as tree
./rat data.json

# View CSV as table
./rat data.csv

# View compressed file
./rat archive.tar.gz

# View image (if terminal supports it)
./rat image.png

# Line range with numbers
./rat --lines=10-50 -n README.md

# Use custom language config
./rat -c ~/.config/rat/my-languages.json code.custom

Flags at a Glance

🔌 SSH Support

View files on remote servers without manually SSHing:

# Using SSH key
rat -S -L lilith@192.168.50.127:22 -K ~/.ssh/lilith-devbox -l "~/code/lsd/lsd.cr"

# Using password (prompts if not provided)
rat -S -L user@example.com:22 -l "/var/log/app.log"

# Multiple files
rat -S -L user@server:22 -K ~/.ssh/key file1.cr file2.rs

🎨 Language Support

Supports 15+ languages out of the box:

• Crystal, Ruby, Rust, Python
• JavaScript, TypeScript, Go, C, C++, Java
• Shell (bash/zsh), YAML, JSON, Markdown
• HTML, CSS, SQL

Custom Language Configuration

Create ~/.config/rat/languages.json:

{
  "languages": [
    {
      "name": "mylang",
      "extensions": [".ml"],
      "shebangs": ["mylang"],
      "keywords": ["func", "var", "if", "else"],
      "comment_single": "//",
      "string_delimiters": ["\""],
      "number_pattern": "\\b\\d+\\b"
    }
  ]
}

Then use:

rat -c ~/.config/rat/languages.json myfile.ml

📦 Archive Support

Automatically detects and handles compressed files:

# Gzip
rat file.gz

# Bzip2
rat archive.bz2

# Tar (shows contents)
rat package.tar

# Zip (shows contents)
rat bundle.zip

Supported formats: .gz, .bz2, .tar, .zip, .tgz, .tbz2, .xz, .lz

📊 Structured Data Viewing

JSON Tree View

rat data.json

Output:

├─ name: "John Doe"
├─ age: 30
└─ address:
   ├─ street: "123 Main St"
   └─ city: "Springfield"

CSV Table View

rat data.csv

Output:

Name          │ Age │ City
──────────────┼─────┼──────────────
John Doe      │ 30  │ Springfield
Jane Smith    │ 25  │ Boston

🎭 Git Annotations

View files with git blame information:

rat -g -n main.cr

Output:

a3f2c8d1 John Doe     2025-01-15 │   1  require "./lib/rat/cli"
a3f2c8d1 John Doe     2025-01-15 │   2
b7e4f9a2 Jane Smith   2025-01-20 │   3  Rat::CLI.run(ARGV)

🖼️ Inline Image Display

Supports multiple terminal graphics protocols:

• Kitty Graphics Protocol (kitty terminal)
• iTerm2 Inline Images (iTerm2)
• w3m (terminals with w3m support)
• Sixel (terminals with sixel support)

rat screenshot.png
rat logo.jpg
rat diagram.svg

Supported formats: .jpg, .jpeg, .png, .gif, .webp, .svg, .ico, .bmp

If your terminal doesn't support graphics, rat shows metadata instead.

🔧 Plugin System

Create custom renderers using JSON-RPC protocol.

Plugin Directory Structure

~/.config/rat/plugins/
├── my-renderer.json       # Plugin config
└── my-renderer            # Executable

Plugin Config (my-renderer.json)

{
  "name": "my-renderer",
  "version": "1.0.0",
  "executable": "my-renderer",
  "file_types": [".custom"],
  "description": "Custom file renderer"
}

Plugin Executable

Must accept JSON-RPC requests on stdin:

{
  "jsonrpc": "2.0",
  "method": "render",
  "params": {
    "path": "/path/to/file.custom",
    "content": "file contents..."
  },
  "id": 1
}

And return:

{
  "jsonrpc": "2.0",
  "result": "rendered output",
  "id": 1
}

List Plugins

rat --list-plugins

🧱 Design Philosophy

• Composable & Pipeline-Safe - default to raw output when piped
• Progressive Enhancement - streaming first, rich UI only when terminal-attached
• Type Safe - Crystal's compile-time type checking prevents runtime errors
• Secure by Default - input/output sanitization, path validation
• Extensible Architecture - plugins and custom language configs
• Zero Configuration - works out of the box with sensible defaults

📂 Project Structure

rat/
├── main.cr                      # Entry point
├── shard.yml                    # Crystal dependencies
├── config/
│   └── languages.json           # Default language configs
├── lib/
│   ├── rat/
│   │   ├── cli.cr               # CLI logic & argument parsing
│   │   ├── reader.cr            # Safe file/stdin reading
│   │   ├── formatter.cr         # Output formatting
│   │   ├── ssh_client.cr        # SSH file fetching
│   │   ├── archive_reader.cr    # Archive handling
│   │   ├── image_viewer.cr      # Inline image display
│   │   ├── structured_viewer.cr # JSON/CSV rendering
│   │   ├── git_annotator.cr     # Git blame integration
│   │   └── plugin_manager.cr    # Plugin system
│   └── internals/
│       ├── highlighter.cr       # Syntax highlighting engine
│       └── language_config.cr   # Language configuration
└── spec/
    ├── spec_helper.cr
    └── spec_highlighter.cr

🔒 Security Features

• Path Sanitization - prevents directory traversal attacks
• Input Validation - all user input is validated and sanitized
• Output Sanitization - strips control characters from output
• File Size Limits - warnings for very large files
• SSH Key Verification - secure SSH authentication
• Type Safety - Crystal's type system prevents entire classes of bugs

🎯 Use Cases

• Development - syntax-highlighted code viewing with git context
• DevOps - view logs on remote servers without SSH session
• Data Analysis - quick CSV/JSON inspection
• Documentation - view markdown files with proper formatting
• Debugging - inspect compressed logs and archives
• System Administration - remote file inspection with annotations

📈 Roadmap

• SSH support for remote files
• Extended language syntax support
• Type-safe implementation
• Input/output sanitization
• Git annotations support
• Archive/compression support
• Structured data viewers (JSON, CSV)
• Plugin architecture (JSON-RPC)
• Inline image preview support
• --follow / -f mode for live-tail with highlighting
• Multi-file diff view
• Syntax theme customization
• WASM plugin support
• Performance profiling mode
• Configurable key bindings

🤝 Contributing

Contributions are welcome! Areas for improvement:

• Additional language syntax definitions
• New image display protocols
• Plugin examples
• Performance optimizations
• Documentation improvements

Please open issues for bugs or feature requests, and submit pull requests with tests.

📝 License

This project is licensed under the MIT License. See the LICENSE file for details.

🙏 Acknowledgments

Built with:

• Crystal Language - Fast, type-safe language
• ssh2-cr - SSH2 protocol support
• crystal-compress - Compression support

---

Made with ❤️ for developers who live in the terminal.

Author: Lily Parker okavatti@proton.me