Watchman

watchman Plugin

Watchman -- a file watching service by Facebook for tracking changes and triggering actions when files change.

Commands

Watching

• watchman watch start — Start watching a directory for changes
• watchman watch list — List all watched directories

Changes

• watchman changes since — Query changes since a given timestamp

Triggers

• watchman trigger add — Set up a trigger to run a command on file changes
• watchman trigger list — List triggers for a watched directory

Utility

• watchman self version — Print watchman version
• watchman _ _ — Passthrough to watchman CLI

Usage Examples

• "Watch this directory for changes"
• "What files have changed since yesterday?"
• "Set up a trigger to rebuild when source files change"
• "List all directories being watched"

Installation

brew install watchman

Or on Linux:

apt-get install watchman

Examples

# Print watchman version
watchman self version

# Start watching a directory
watchman watch start /path/to/project

# List watched directories
watchman watch list

# Query changes since a timestamp
watchman changes since /path/to/project 2024-01-01T00:00:00

# Set up a trigger
watchman trigger add /path/to/project rebuild "*.js" -- npm run build

# List triggers
watchman trigger list /path/to/project

# Any watchman command with passthrough
watchman _ _ log
watchman _ _ shutdown

Key Features

• File watching — Efficient recursive directory watching
• Change tracking — Query changes by timestamp or subscription
• Triggers — Run commands automatically on file changes
• Cross-platform — Works on macOS, Linux, and Windows
• Efficient — Uses OS-native file watching (inotify, FSEvents, etc.)

Notes

• Watchman daemon must be running for most commands
• Start daemon with watchman watch /path (auto-starts daemon)
• Used by React Native, Buck, and other large build systems
• Configuration stored in ~/.watchman/