{
  "00123" => {
               "File 1" => "www.site.com/path/to/file/file.pdf",
               "File 2" => "www.site.com/path/to/file/file.pdf",
             },
  "00124" => {
               "File 1" => "www.site.com/path/to/file/file.pdf",
               "File 6" => "www.site.com/path/to/file/file.pdf",
             },
  "00125" => {
               "File 2" => "www.site.com/path/to/file/file.pdf",
               "File 7" => "www.site.com/path/to/file/file.pdf",
             },
}

##</code><code>##

open my $fh, ">:encoding(UTF-8)", "output.csv" or die "output.csv: $!";
my $csv = Text::CSV->new({binary=>1, auto_diag=>2, eol=>$/,
	always_quote=>1 });
$csv->print($fh, ["sku", @columns]);
for my $sku (sort keys %$itms) {
	$csv->print($fh, [$sku, map { $itms->{$sku}{$_} } @columns ]);
}
close $fh;