The Listen gem listens to file modifications and notifies you about the changes.

Features:
- Works everywhere!
- Supports watching multiple directories from a single listener.
- OS-specific adapters for Mac OS X 10.6+, Linux and Windows.
- Automatic fallback to polling if OS-specific adapter doesn't work.
- Detects files modification, addidation and removal.
- Checksum comparaison for modifications made under the same second.
- Allows supplying regexp-patterns to ignore and filter paths for better
  results.
- Tested on all Ruby environments via travis-ci.

WWW: https://github.com/guard/listen
RG:  https://rubygems.org/gems/listen