There are various tricksy ways of trying to count the number of zeros and ones in a byte, but a lookup table is small and simple:

  my @ones = (0);
  push @ones, map $_ + 1, @ones for 1 .. 8;
  my @zeros = map 8 - $_, @ones;
  ...
  read($fh, $buf, 1) or die ...;
  my $val = ord($buf);
  printf "%08b has %s ones and %s zeros\n", $val, $ones[$val], $zeros[
+$val];
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