Learning Perl chpt.13 problem

I don't understand the regex s#.*/##s (given as part of the solution to problems 2 and 3) more specifically, I don't know what the last 's' does to the regex. __ Do You Yahoo!? Spot the hottest trends in music, movies, and more. http://buzz.yahoo.

don't understand word boundary

on page 83 of Learning Perl, they give a regex example: /abc\bdef/; #never matches (impossibe for a boundary there) Could someone please explain this to me clearly so I can actually understand word boundaries? thanks... __ Do You Yahoo!?