my $atleastone = 1;
  while ($atleastone) {
    $atleastone = 0 ;

    my $l = '' ;
    foreach my $op (@handles) {
      my $c2 ;
      ++$atleastone and (undef, $c2) = split if defined($_ = <$op>) ;   
      $l .= ($c2 || "0") . "\t" ;
    } ;
    chop $l ; # Discard trailing "\t"
    print OUTFILE "$l\n" ;
  } ;