AppleScript: The Definitive Guide, 2nd Edition

Folder Actions

A folder action involves a script being called automatically when certain events take place in a designated folder in the Finder. A script to be used as a folder action does not live in the folder with which it is associated; rather, it should live in your user library, at ~/Library/Scripts/Folder Action Scripts. Alternatively, such a script may live in the top-level /Library/Scripts/Folder Action Scripts, where you'll find some useful examples of folder action scripts, but the location in your user library is the default.

Because the script and the folder are in different places, an extra step is required in order to form the explicit association between a particular script and a particular folder. In essence, this association is the folder action. To form such an association is to attach the script to the folder; to break the association is to remove the script from the folder. The script is not actually moved; attachment and removal are conceptual, not physical. Attachment and removal are implemented through the System Events application (see "System Events" in Chapter 23). System Events associates a folder with a script through a folder action object. These folder action objects are maintained as top-level elements of the System Events application class. System Events is then responsible for watching those folders to see whether an appropriate event takes place in the Finder, and, when it does, for sending the corresponding messages to any attached scripts. System ...