foreach my $file ( sort glob("*.csv") ) {

  $filenum++;
  open my $fh, "<", $file or die $!;

  while ( my $line = <$fh> ) {
    chomp $line;
    my ( $row_val, @values ) = split /,/, $line;
    $row_val{$row_val} = 1;
# delete   $data{$filenum}{$row_val} = \@values;
# add these 3 lines
    for my $c (1..@values){
      $data{$row_val}[$c-1] .= $values[$c-1];
    }
 }
 close $fh;
}

foreach my $row_val ( sort keys %row_val ) {
	print join ",",$row_val,@{$data{$row_val}},"\n"
}