This is my "There's more than one way to do it", its prolly insane and stupid. But I did it anyways.

p.s. some borrowed methodology from merlyn.

#!/usr/bin/perl -w

use strict;
use File::Copy qw(copy);

die("Usage: $0 <src> <dst>\n") unless($#ARGV==1);
-d or die("$_ is not a directory") for(@ARGV);

s/\/$// for(@ARGV);
for(glob("$ARGV[0]/*"),glob("$ARGV[1]/*")) {
 copy("$ARGV[0]/$_","$ARGV[1]/$_") or warn("$!: $ARGV[0]/$_\n")
  if(s/$ARGV[0]// && -f "$ARGV[0]/$_" && !-e "$ARGV[1]/$_");
 unlink("$ARGV[1]/$_") or warn("$! unlinking $ARGV[1]/$_\n")
  if(s/$ARGV[1]// && -f "$ARGV[1]/$_" && !-e "$ARGV[0]/$_" );
}
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/****************************/
  jason@gost.net, wh@ckz.org
    http://jason.gost.net
/*****************************/
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