use File::Copy;

my ($src,$dst) = @ARGV;

-d or die "$_ is not a directory" for $src,$dst;
## first pass, copy anything not there...
opendir SRC, $src or die "cannot opendir $src: $!";
for (readdir SRC) {
  next unless -f "$src/$_";
  next if -e "$dst/$_";
  print "copying $src/$_ to $dst/$_...\n";
  copy "$src/$_", "$dst/$_" or warn "Cannot copy!";
}
closedir SRC;
## now delete the ones that don't belong there
opendir DST, $dst or die "Cannot opendir $dst: $!";
for (readdir DST) {
  next unless -f "$dst/$_";
  next if -e "$src/$_";
  print "deleting $dst/$_...\n";
  unlink "$dst/$_" or warn "Cannot unlink: $!";
}
closedir DST;