$/ = \ 7 * 1024; # read 7 K records.

while (<>) {  # read record into $_
   my $info = substr($_, 0, 1000); # put first 1000 bytes in $info
   my $lab = substr($_, 1000, 1000);
   my $diagnosis = substr($_, 20000, 49999);
   my $last = chop; # get last character

   # now do stuff with that data

}