!/usr/bin/perl -w -p 
s {
  ^(\*+) # look for stars at the beginning of line
}{
  my $n = length($1); # get number of stars
  @l[$n+1..$#l] = (0)x($#l-$n) if $n < $o; # @l is global
  $l[$n]++;
  $o = $n; # $o is global
  join(".",@l[1..$n]); # returning this
}ex;