use strict;

BEGIN
  {
  use constant     ROTATE => 1; 
  use constant       HOLD => 2; 
  use constant      FLASH => 3; 
  use constant  NUM_MODES => 3;
  # etc...
  }

my %modestring = 
  (
  ROTATE => "a",
    HOLD => "b",
   FLASH => "c",
  # etc...
  );

  my $mode = int(rand NUM_MODES) + 1;
  print "random mode string is ", $modestring{$mode} || "empty", "\n";   
  print "string for 1 is ", $modestring{1} || "empty", "\n";   
  print "string for ROTATE is ", $modestring{ROTATE} || "empty", "\n";   

random mode string is empty
string for 1 is empty
string for ROTATE is a