Your code has baffled me. What is this meant to do? We might be able to answer your questions better. Issues:

1. You test $i, you incremnt $i, but you never actually use $i.
2. ($a, $b, $c, $d) = split(/[\t]/, $stuff[89..93]); should probably be: ($a, $b, $c, $d) = split(/[\t]/, @stuff[89..93]); - except if you want the 90th through 94th values of @stuff put into the four variables ($a, $b, $c, $d), you don't need the split, and you only need to do it once.
3. Whatever that line of code does, it does it 90 times (for $i = (0..89)) - is this what you wanted?

Give us a small piece of real code and tell us what you wanted it to do and we might be able to help. As it stands, I personalkly can olnly say: perldoc perlsyn .

--Bob Niederman, http://bob-n.com