use Date::Calc qw/ check_date Localtime /;

my $date = shift @ARGV;
my @date = split '-', ( $date || '2002-02-31' ); # Naturally, this date is invalid
unless (check_date(@date)) {
    carp( 'Invalid date supplied from command line - Overriding with current date' ) if $date;
    @date = (Localtime)[0..2];
    $date = join '-', @date;
}