in reply to Trigger the execution!
The closest thing I can think of would be to run your script (or a wrapper) as a cron job (Unix/Linux)or a scheduled task (Windows) and have it take whatever action you want if conditions are met (i.e. if a file has been modified in the last hour or whatever you would look for).
Not instant, but you can have it run fairly frequently. Might work for you, depending on exactly what your application is.