You are so close on this one - From perlsub ...

Any arguments passed to the routine come in as the array @_. Thus if you called a function with two arguments, those would be stored in $_[0] and $_[1]. The array @_ is a local array, but its elements are aliases for the actual scalar parameters.

So, if you are wanting to access the passed parameters directly, you will want to use $_[0] or alternately shift off values from the @_ array. eg.

sub get_long_count {
    my ($dd, $mon, $yyyy, $bc) = split /-/, $_[0], 4;
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