in reply to Trying to allow user-customizable prompts in a chat program

I'd use a hash: 
my %data = (
  RN => 'Joe',
  LOC => '3rd floor',
  UN => 'juser',
);

my $prompt = "-RN- \@ -LOC-";
$prompt =~ s/-([^-]+)-/$data{$1} || "-$1-"/eg;

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Update: Here's another way: 
%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]);

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