Watching for changes to the filesystem?

Question

Hi,
Is there an automator object that will allow me (through Applescript perhaps) to receive notifications of when something in a certain part of the filesystem changes?
For example, I would like to be notified when a new document is added to the Documents directory (likewise I'd like to be notified when a document is removed from that directory).
Thanks,
BT

Answer 1

Hi BT
AppleScript has a mechanism called Folder Actions, which will do exactly what you require. Automator workflows can also be saved as Folder Actions, but they run more slowly for reasons I'll explain later.
A Folder Action script runs when you make a change to a folder to which the script has previously been attached. The possible changes are: opening the folder window, closing the folder window, moving the folder window, adding items to the folder and removing items from the folder. The last two are what you're looking for.
Only these five changes will trigger a folder action; folder actions don't run if you edit or update a file within a folder.
Folder actions aren't recursive: if you add items to a sub-folder of the folder to which the action is attached, the action attached to the parent folder won't run.
Here's an AppleScript that will do what you want, with the notification in the form of a dialog.
--begin script
on adding folder items to this_folder after receiving these_items
set folder_name to name of (info for this_folder)
set item_count to (count these_items) as string
display dialog item_count & " Items were added to " & folder_name & "!" with icon note buttons {"OK"} default button 1
end adding folder items to
on removing folder items from this_folder after losing these_items
set folder_name to name of (info for this_folder)
set item_count to (count these_items) as string
display dialog item_count & " items were removed from " & folder_name & "!" with icon caution buttons {"OK"} default button 1
end removing folder items from
-- end script
Copy and paste this script into a new Script Editor document, and save the script into the folder ~/Library/Scripts/Scripting Additions/ (create it if it doesn't already exist).
Control-click on the folder you want to run the action, and choose Enable Folder Actions if they aren't already enabled. Control-click on the folder again, and choose Attach a Folder Action... Navigate to the folder where you saved your script, and choose the script. Drag items in and out of the folder and see what happens.
The dialog can be replaced by any AppleScript commands you like: the script could send an email, log the change to a text file, create a new document in a scriptable application, log the user out, play their top-rated iTunes tracks...
Hope that gets you started. Using Automator would be slower because folder actions created in Automator simply launch a separate Automator workflow application, which then runs the commands which I've scripted directly. This just puts another application in the way of getting the job done.
Why not post in the AppleScript forum if you want to know more?
Cheers,
H