use strict;
my @strs = ('ABC','aZ','CC','AZ','ZZ','?A','W1','A ','  ','..','A','1','');
foreach (@strs) {
   if (/^[A-Z]{2}$/) {
      print "PASS: ";
   } else {
      print "## FAIL: ";
   }
   print "'$_'\n";
}