What's the tool that can do some actions when a file is copied? I use Cmd+L to make a alias, and the alias has "alia" appended to the original file name. I move the link to a directory, then remove the "alias" part manually.

Is there a tool that can do this kind of automatically? I mean, if a tool can catch the event a file is copied to a specific directory to call a tool (python, ruby or applescript) with a parameter, I can easily rename the file name.

ADDED

Thanks to Ben and Dori, I could get it working.


Go to /Library/Scripts/Folder Actions directory to Folder Actions Setup.
Run Automator
Utilities -> Run Shell Script
Use python as a shell, and pass input should be as arguments
Run the following code



import sys
import os

for f in sys.argv[1:]:
    (name, ext) = os.path.splitext(f)
    newname = "%s%s" % (name, ".pdf")
    os.rename(f, newname)


Philip's method should work, but I think Automator is easier to get it work. 
On my Snow Leopard, I couldn't see the folder action context menu.
In addition to Applescript, Automator allows you to create Folder Actions as well, at least in 10.6. (This should have been a comment on Philip's post, but I don't quite have enough rep for that yet.)