File Watcher

File Watcher

Use Claude Code's FileChanged and CwdChanged hooks to create reactive workflows that respond to file system changes.

Trigger

Use when:

• Setting up auto-reload for config changes
• Watching for dependency updates
• Monitoring build output
• Creating reactive development workflows

How File Watching Works

Claude Code's SessionStart and CwdChanged hooks support returning watchPaths to register file watchers. The current cwd-changed.js script focuses on env injection; to add watch registration, your hook script must output this JSON structure:

{
  "hookSpecificOutput": {
    "hookEventName": "SessionStart",
    "watchPaths": [
      "/absolute/path/to/.env",
      "/absolute/path/to/package.json"
    ]
  }
}

When watched files change, the FileChanged hook fires with:

{
  "hook_event_name": "FileChanged",
  "file_path": "/path/to/changed/file",
  "event": "change"
}

Environment Injection

CwdChanged and FileChanged hooks can write to CLAUDE_ENV_FILE to inject environment variables into subsequent Bash commands: