Thanks for your reply,
thought that the -w would trigger warnings as well. Anyhow I did put use warnings; in my code but no warnings.
guess I'm losing my way a bit.. should it look like this?

my $row;
local $"='|'; print STDERR "<@$row>\n";
while ( my $row = $csv_in->getline($fh_in) ) {
    $csv_out->print( $fh_out, [ @$row[ 2, 3, 0, 4 ], ] );
}
print STDERR "<$row>\n";
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I get
Can't use an undefined value as an ARRAY reference at but I'm not sure I put the code in the correct way. Trying to figure this out...