You can use a hash slice for the first part, and just a foreach loop for the second part, but the key is to just store the key names so they aren't repeated -- also you now just have a single place to make changes in, so much easier to maintain.

    my %fields;
    #$csvIn is a Text::xSV object.
    my @field_names = qw/ partner kampagne keywordCluster keyword clic
+ks leads
        orders jaronVerguetung partnerVerguetung profit /;
    while ($csvIn->get_row()) {
        @fields{@field_names} = $csvIn->extract( @field_names );
        foreach my $k ( @field_names ){
          $fields{$k} = "" unless defined $fields{$k};
        }
    }
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Update: changed @k to @field_names to be a little more descriptive.