I think you should pass $today and $yesterday to the print_report subroutine: print_report($today, $yesterday);

The same should be done with write_benchmark, you should pass the hash reference to the sub instead of relying on a global variable: write_benchmark($today);

Your programs will be more readable, maintainable, and scalable.

Inside print_report, access them like this:

sub print_report {
   my ($today, $yesterday) = @_;

}
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