%cat = (
   'C[AEIOU]NWAY' => 'AAA',
   '(?:BOSTON|CHICAGO)' => 'BBB',
   '(?:LAS VEGAS|NEVADA)' => 'CCC',
   '(?:DALLAS|AUSTIN)' => 'DDD',
   '(?:NASHVILLE|M[AEIOU]MPHIS)' => 'EEE'
);
$var = "CHICAGO";
@keys =  keys %cat;
$re = "(".join(")|(", @keys).")";
if ($var =~ /$re/o) {
  for ( 1 .. @keys) { 
    print "$_:", $$_, " - ",  $keys[$_-1], "\n" if defined $$_ }
}