are you asking for if statements?

if(condition) {do the thing;}

I know this is trivial to do programmatically, but I was looking for a way this will be handled by the filesystem. For instance, if I have some processes generating log files, and I have a script that converts them to html, I wanted the script to be called every time a log file is updated, without having a daemon running in the background to monitor the directory, just some filesystem mount. This would have made some deployments easier.