while (length $input > 6){
   my $front = substr($input, 0, 6);
   $input    = substr($input, 6);
   push @sets_of_six, $front;
}

##</code><code>##

while (length $input > 6){
   my $front = substr($input, 0, 6, '');
   push @sets_of_six, $front;
}

##</code><code>##

while (length $input > 6){
   push @sets_of_six, substr($input, 0, 6, '');
}