Families of Variable Names

Glancing over the program, this is the first thing you see

     26   SWITCH: {
     27       $chain_number==1 && do {
     28         @chain1 = split (//,$chain_input);
     29         $scan_chain_length1 = @chain1; };
     30       $chain_number==2 && do {
     31         @chain2 = split (//,$chain_input);
     32         $scan_chain_length2 = @chain2; };
     33       $chain_number==3 && do {
     ...
     45       $chain_number==7 && do {
     46         @chain7 = split (//,$chain_input);
     47         $scan_chain_length7 = @chain7;
     48         &printout;
     49       };

As usual, we will replace these with an array of arrays

        $chain[$chain_number] = [split //, $chain_input];
        $scan_chain_length[$chain_number] = @{$chain[$chain_number]};
        &printout if $chain_number == 7;

23 lines become 3