# sketch, totally untested

# define groups
my %p = (
   month => '\w+',
   ...
);
 
# wrap named groups later
while ( my ($k,$v) = each %p ) {
   $v = qr{(?<$k>)$v};
}

# compose patterns
my $re_dn = qr{^$p{month} $p{day} ...};