# Create ARRAYref to list of 7 elements, with first element "",
    # remaining 6 elements copied from @fields.
    $file2{$id}=["",@fields];
    $file3{$id}=["",@fields];
...
    # trying to access 6th element of $file2{$id} as a list, but it's
    # an ARRAYref to a list with 7 elements...
    my @fields2=$file2{$id}[5];
    my @fields3=$file3{$id}[5];

##</code><code>##

    # just hang onto the ARRAYref returned from $csv->getline(),
    # unless it doesn't want us to.
    $file2{$id}=$row; 
    $file3{$id}=$row;
...
    # You really did want the 6th column, right?
    my $fields2=$file2{$id}->[5];
    my $fields3=$file3{$id}->[5];

##</code><code>##

    # Create list with one element as a string concat looking like
    # "ARRAY(0x141ecf8)\tARRAY(0x141edd0)\tARRAY(0x141ee48)"
    my @printline= ( $fields_ref."\t".\@fields2."\t".\@fields3;
    $csv->print ($FILE4,\@printline);

##</code><code>##

    # List with 8 elements
    my @printline= ( @fields, $file2{$id}->[5], $file3{$id}->[5] );
    $csv->print ($FILE4,\@printline);