[ltp] Syncing from TP HDD to USB key

[Bob Alexander]

I would like to perform a bi-directional syncing of the contents of my 
USB key with a given directory (in which I could be giving the command 
line command) with the aim of copying files between the key to the hard 
disk only where NEWER versions of existing files are to be found.

Let me explain with an example:

Key         HDD
A1          A2
B2          B1
C1          D1

In the above example A2 stands for a newer version of file A (A1 an older).

In this example I would like to have:

A2 copied onto A1
B2 copied onto B1

but NOT
C1 to HDD

and NOT
D1 to Key.

Any ideas on the simpler but dependable way of doing this ? An 
interaction for confirmation would be useful especially if squelchable.

Thank you very much,
Bob