I've never written a script for OS X, and I don't really know which scripting tool i'll use for this task.
Here's a pseudo code for the script I want to build :
whenever a new file X is added to the directory D do: copy X paste X to the directory B
I don't want someone to code this for me, I want to know what tool (language maybe) should I use to write this script, and how to make OS X runs it whenever the event occurs.
I don't know what to tag this. Please contribute. Please redirect if this isn't the right forum for this question.