I don't exactly know how should I use Data::Dumper

Best to have a quick look at the Data::Dumper documentation. The Dumper() function is exported by default and gives a pretty crude picture of the data. Give it an array and it will treat each element as a separate variable but give it a reference to the array and you see an anonymous array. Dump() and its faster but not always available sibling Dumpxs() are fiddlier but more useful as they can give a more accurate picture.

Here's a brief example.

johngg@shiraz ~ $ perl -Mstrict -Mwarnings -MData::Dumper -E '
my @atts = qw{ att1 att2 att3 };
say Dumper( @atts );
say Dumper( \ @atts );
say Data::Dumper->Dump( [ \ @atts ], [ qw{ *atts } ] );
say Data::Dumper->Dumpxs( [ \ @atts ], [ qw{ *atts } ] );'
$VAR1 = 'att1';
$VAR2 = 'att2';
$VAR3 = 'att3';

$VAR1 = [
          'att1',
          'att2',
          'att3'
        ];

@atts = (
          'att1',
          'att2',
          'att3'
        );

@atts = (
          'att1',
          'att2',
          'att3'
        );
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I hope this is helpful.

Thank you for explanation. When I use Dump function on attachments array I get string "@attachments = ();". I really don't know what kind of anomaly is this. I just found out that I can get nothing from request, not only file.