use DateTime;
my $yyyy = 2015;
my $mm = 05;
my $date = DateTime->new(year => $yyyy, month => $mm);
$date->subtract(days => ($date->day_of_week - 2) % 7 - 7 * 2);
print "$yyyy年$mm月的第二個禮拜二是$date\n";

use Date::Manip::Base;
my $dmb = new Date::Manip::Base;
my $yyyy = 2015;
my $mm = 5;
my $ymd = $dmb->nth_day_of_week( $yyyy, 2, 2, $mm);
printf "$yyyy年$mm月的第二個禮拜二是%s\n", join '-', @$ymd;

use Date::Manip::Date;
my $date = new Date::Manip::Date;
$date->parse('Second Tuesday in Jul 2015');
print $date->printf('%Y-%m-%d'); # prints 2015-07-14