[ale] polling directories

[jb at sourceillustrated.com (John Wells)]

I'd like to watch a few specific directories on a Linux system for new
files.  Each time a user copies a file into the directory, I'd like to
specify a script that will run, using that file as its argument.

I can write this myself, but I wonder if someone hasn't already invented
this wheel?  Is anything approaching a standard way to do this?

Thanks,
John