Styjun

I'm following @zdim's recursive solution in this post
fastest way to sum the file sizes by owner in a directory to get my file sizes summed up by year-month

perl -MFile::Find -E' use POSIX;
 $dir = shift // "."; 
 find( sub 
 return if /^..?$/; 
 my ($mtime, $size) = (stat)[9,7];
 my $yearmon = strftime "%Y%m",localtime($mtime);
 $rept$yearmon += $size ;
 , $dir ); 
 say ("$_ => $rept$_ bytes") for sort keys %rept
'

It gives results like this.

201701 => 7759 bytes
201702 => 530246 bytes
201703 => 3573094 bytes
201704 => 425827 bytes
201705 => 3637771 bytes
201706 => 2325391018 bytes
201707 => 127005 bytes
201708 => 2303 bytes
201709 => 231465431 bytes
201710 => 273667 bytes
201711 => 6397659 bytes
201712 => 333587 bytes
201802 => 874676 bytes
201803 => 147825681 bytes
201804 => 84971454 bytes
201805 => 3483547 bytes
201806 => 8004797 bytes
201807 => 184676 bytes
201808 => 1967947 bytes
201809 => 1592310 bytes
201810 => 24176 bytes
201811 => 883378 bytes
201812 => 6661592 bytes
201901 => 33979401 bytes

But I need to include year-wise totals after printing all available months in a given year, like below

201710 => 1111 bytes
201711 => 2222 bytes
201712 => 3333 bytes
2017 => 6666 bytes ( summed up )
201803 => 11111 bytes
201809 => 22222 bytes
2018 => 33333 bytes ( summed up )

How do I get that?. There might be blanks in a year-month and it need not end with month 12 for every year.

Two small changes will do the trick.

perl -MFile::Find -E' use POSIX;
 $dir = shift // "."; 
 find( sub 
 return if /^..?z/; # Fixed $ -> z
 my ($mtime, $size) = (stat)[9,7];
 my $yearmon = strftime "%Y%m",localtime($mtime);
 $rept$yearmon += $size;
 $reptsubstr($yearmon, 0, 4) += $size; # <---
 , $dir ); 
 say "$_ => $rept$_ bytes"
 for sort "$a99" cmp "$b99" keys %rept; # <---
'

Given that you've built the %rept hash in the first part of your code, the display section should be something like this:

# Keep track of current year and current year total
my ($year, $year_total);

for (sort keys %rept) 
 # Get the year from the current record
 my $this_year = substr($_, 0, 4);
 # If the year has changed, then print a total line
 # and reset the year total.
 if (defined $year and $year ne $this_year) 
 say "$year => $year_total bytes";
 $year_total = 0;
 
 # Add to the year total and store the current year
 $year_total += $rept$_;
 $year = $this_year;

 say "$_ => $rept$_ bytes";


# Final year total line
say "$year => $year_total bytes";