Triggering scripts to run when a file or folders change is a common advanced task. Recent applications like Dropbox and BitSync have grown from the days of rsync magic, but what about triggering code when a sync occurs. It could be as simple as emailing a photo to your parents once 5 pictures are updated in Dropbox or as advanced as rebuilding a static blog based on content changes of configuration files in a folder. This post focuses on the Linux tool for handling these events that relies on inotify; but there are similar (not covered here) ways on BSD/OSX/Windows too (FSEvents/kqueue).
I ran into this when setting up a Dropbox sync to cause a Grunt process to build a stage server. The Dropbox sync would need to trigger an Assemble.io process to turn Yaml files (that are held in the Dropbox path) into HTML.
Inotify is the systems way to event filesystem changes, but to be able to tap into inotify events it’s easiest to install another daemon called incrond (inotify cron daemon) that abstracts inotify system calls in a manageable way.