my $str = 'xx556xx';
my @x = grep --$|, $str =~ m/((.)\2*)/g;
report('pre-deincrement', @x);
my @x = grep $|--, $str =~ m/((.)\2*)/g;
report('post-deincrement', @x);
my @x = grep ++$|, $str =~ m/((.)\2*)/g;
report('pre-increment', @x);
my @x = grep $|++, $str =~ m/((.)\2*)/g;
report('post-increment', @x);

sub report{
  my ($type, @y) = @_;
  print "\n\nautoflush = ", $|, " , $type\n";
  print join ',', @y;
}