For example:
sub total_size_and_print {
my ($dir, @sizes) = @_;
my $total = -s $dir;
$total += $_ for @sizes;
printf "%-6d %s\n", $total, $dir;
return $total;
}
walk_tree($DIR, sub { -s $_[0] }, \&total_size_and_print);
The result:
86 ./slides/Advanced 508 ./slides/Tricks 595 ./slides 596 .