Request for comments/ clues on simple text manipulation script

[NovMonk]

Greetings, Kind Monks,

First, I have a confession-- about a month ago I received some great clues from graff, Belgarion, cLive;-), revdiablo, and punkish concerning this node. I usually thank people who help me out, but this time, illness, life and other misfortunes delayed me. So, I say now, thanks very much, you fellows are a credit to the community, and I'm really sorry for not saying it sooner.

Now for my question. I've written a script that works interactively with vi to add some code to a text file. The text file starts out something like this:

l ban
n10total
n01first line
n01second line
--- (more lines)
n01fifteenth line (approx)
l ban2
... (variations on above)

When I get done, I get this:

l ban1
tstat propmean;elms=ABC (etc);
n10
n01first line;ID=A
n01second line;ID=B
--- (etc)
n01fifteenth line;ID=Q
l ban2
tstat (line as above)
n10total
n01first line;ID=A
(etc.)

What I need help with is this-- I'd like each tstat line to only show the letters I'm using in the n01 lines below it, for the stuff between one l ban line and the next. I'd also like it to error out if the number of n01 lines in any section (defined as one line beginning with l and the next such line-- there can be any number of such sections in the file, though probably, not more than 3 or 4) exceeds the number of available letters in my array @letters. And I'd like it to do this without munching my text file.

Here's my code:

#!/usr/bin/perl
use warnings;
use strict;
use diagnostics;
#array @letters is all letters except O,I,L (not used in this process)
my @letters = qw/A B C D E F G H J K M N P Q R S T U V W X Y Z/;
my $count = 0;
while (<>){
  if (/^[Ll]/){
    s/\n/\ntstat propmean;elms=AB,CDEFGHJKMNPQRSTUVWXYZ;clevel=95,90;p
+ropcorr\n/g;
    $count = 0;
  }
  if (/^[Nn]01/){
    s/\n/;ID=$letters[$count]\n/;
    $count++;
  }
  print $_;
}

It's very simple stuff, but I am still fairly new and clueless. I assume I need to completely revamp my thinking, if my two enhancements are possible at all. I would appreciate not only ideas but explanations of what I could be doing better. And this time, I'll be more prompt in thanking you for the wisdom.

Pax,

NovMonk