Mirror files to a directory

easy hunh ! but wait there's catch

[vabtz]

I have 2 directories we'll call them A and B

directory A has all the files
directory B has some files from A

I want to copy files from A to B but only if they exist already in B. I also want to do this recursivley

any easy onliners anyone can think of for this?

[vabtz]

oh wait forget it I see the -u option in the cp man page now