%map = (
  UN => 0,
  RN => 1,
  LOC => 2,
);

my $prompt = "-RN- (-LOC-)";
my @user_info = ("juser", "Joe", "3rd floor");
my @slices;

$prompt =~ s{-([^-]+)-}{
  if (exists $map{$1}) {
    push @slices, $map{$1};
    "%s";
  }
  else { "-$1-" }
}eg;

my $output = sprintf($pattern, @user_info[@slices]);