while(<IN>){
     my $line = $_;

     unless ($line =~ /\S/) {
          print STDERR "Skipping line $. (blank)\n";
          next;
     }

     my @fields = split /\t/,$line;

     unless (@fields >= 10) {
          print STDERR "Error: line $.: less than 10 fields: $_\n";
     }

.
.
.