#!/usr/bin/env perl 
use strict;
use warnings;

my $s='IIIIIIIIIIIIIIIIIIIIIIIIIIOOOOOSSSSS';

print "$s: " . ($s =~ tr/M/M/ ? "case1\n" : "case2\n");

$s .= 'M';

print "$s: " . ($s =~ tr/M/M/ ? "case1\n" : "case2\n");