John, I'm really struggling with this - trying to understand his logic and to understand Perl (though it is C like enough to make some sense to me).

After about 3 hrs... I've found the reason for the accidentals not working. He has a section:

  if ($nt < $NumChars - 1) {    
     SWITCH: for (substr($inline,$nt+1,1)) {
         /\(/           && do { $ProcessNow = "Yes"; };
         /\|/           && do { $ProcessNow = "Yes"; };
         /\:/           && do { $ProcessNow = "Yes"; };
         /\[/           && do { $ProcessNow = "Yes"; };
         / /            && do { $ProcessNow = "Yes"; };
         /[A-Ga-gZz]/   && do { $ProcessNow = "Yes"; };
  };
  

What that does is checks the character after the one being currently being worked on. The logic is for example that if the next character is a note, it's time to put all the information (note length, whether an accidental, etc.) into his structure.

The flaw is that certain items like accidentals precede notes. So if you have ^C, the above code sees the next character is a note and decides to move on to the next step.

I've managed to get:
C ^C | D^D E F ^F G ^G | A ^A B c ^c | d ^d e f | ^f g ^g a ^a b |

to display correctly by adding a line after that switch statement to tell it that if the current character is a "sharp", it should set $ProcessNow = "No".

Jon