Q. How do I pass a hash reference to a subroutine in Perl?
A. This can be achieved by preceeding the hash with a slash when passing:
#assume you have a hash
my %results = (start_date => "may 1", end_date => "sep 1");
#pass the hash
test(\%results);
#your subroutine
sub test {
my $ref = shift;
# assign new variable
$ref->{'start_date'} = "new date";
}