You're tripping over a scoping issue thanks to declaring your variable inside your if blocks.

Declaring my $New_mo = ""; before your ifs and removing my from all the assignments in the ifs will fix your problem.

However, there's a much simpler solution to be had using arrays and indicies...

my @months = qw( 
    Jan Feb Mar Apr May Jun 
    Jul Aug Sep Oct Nov Dec
);
my $new_mo = $months[$month];
[download]

Update: D'oh ... can't believe I missed the whole =/== thing! Don't I feel silly...

    --k.