my @month_names = qw( undef, jan feb mar apr may jun jul aug sept oct nov dec );
my @month_days = ( undef, 31, &feb_days, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 );

my $months = {
    name   => { map{ $_, $month_names[$_]} 1..12 },
    number => { map{ $month_names[$_], $_ } 1..12 },
    days   => { map{ $_, $month_days[$_], $month_names[$_], $month_days[$_] } 1..12 },
};

print "Month number 4 is ",   $months->{name}->{4}, "\n";
print "Month mar is number ", $months->{number}->{mar}, "\n";
print "Days in month feb ",   $months->{days}->{feb}, "\n";
print "Days in month 4 ",     $months->{days}->{4},   "\n";


use Data::Dumper;
print Dumper $months;

sub feb_days { check_leap_year( get_year() ) ? 29 : 28 }

sub get_year { (localtime())[5] + 1900 }

sub check_leap_year {
    my $year = shift;
    my $leap_year = 0;
    $leap_year = 1 if $year % 4 == 0;
    $leap_year = 0 if $year % 100 == 0 and $year % 400 != 0;
  return $leap_year;
}