t2: Rerun commands when files change

A fast, efficient file watcher written in Rust that automatically reruns commands when files change.

Overview

t2 is a Rust implementation of the file watcher. It watches files for changes and automatically reruns specified commands, making it perfect for development workflows where you need to rebuild, retest, or recompile after code changes.

Key Features

• Event-based watching: Uses the notify crate for efficient OS-level file system events (no polling!)
• Debouncing: 500ms debounce to avoid running commands multiple times for rapid changes
• Fast: Compiled Rust binary with instant startup and minimal resource usage
• Gaming-themed: Fun output messages (FIGHT!, CONTINUE?, GAMEOVER)
• Smart filtering: Automatically ignores common temporary and binary files
• Cross-platform: Works on macOS, Linux, and Windows

Installation

From crates.io

cargo install t2

From Source

cargo install --path .

Build

cargo build --release

The binary will be at target/release/t2.

Usage

t2 'command' [monitor_path [monitored_path...]]

Examples

Watch Rust files and run tests:

t2 'cargo test' src/

Watch markdown files and rebuild docs:

t2 'make docs' *.md docs/

Watch multiple directories:

t2 'npm run build' src/ static/ templates/

How It Works

1. Startup: t2 scans specified paths and runs the command immediately
2. Watching: Monitors files using OS-level file system events
3. On Change: When a file changes, prints "FIGHT!" and reruns the command
4. Completion: After command finishes, prints "CONTINUE?" and waits for next change
5. Exit: Press Ctrl+C to stop, prints "GAMEOVER"

Ignored File Types

t2 automatically ignores changes to these file types:

• Python bytecode: .pyc
• Editor swap files: .swp, .swo
• Images: .bmp, .jpg, .jpeg, .png, .gif, .svg, .psd, .xcf, .pxm

Improvements Over p2 (Python Version)

• Event-based watching instead of 1-second polling (faster, more efficient)
• Instant response to file changes
• Lower CPU usage (no constant polling loop)
• Faster startup (compiled binary vs interpreted Python)
• Type safety and memory safety from Rust
• Debouncing to handle rapid file changes gracefully

Output Example

$ t2 'echo "Building..."' src/
t2 is watching about 8 files:
src/
FIGHT!
echo "Building..."
Building...
CONTINUE?
src/main.rs changed
FIGHT!
echo "Building..."
Building...
CONTINUE?
^CGAMEOVER

Development

Run Tests

cargo test

Build for Development

cargo build

Build for Release

cargo build --release

Project Structure

t2/
├── Cargo.toml              # Project configuration
├── src/
│   ├── main.rs             # Entry point and orchestration
│   ├── filter.rs           # File ignore patterns
│   ├── scanner.rs          # File discovery
│   ├── executor.rs         # Command execution
│   ├── watcher.rs          # Event-based file watching
└── tests/
    └── integration_tests.rs # Integration tests

License

MIT License

Author

Keith Yang yang@keitheis.org