An arrayref is a scalar value, so you should store it in a scalar variable. There are several ways of dereferencing (turning it into an array) an arrayref. One of the easiest is to prepend the scalar variable that holds an arrayref with the array sigil ("@").

my $fieldNames = $sth->{ NAME_uc };
printf "%15s %12s %12s %22s %9s %5s $5s", @$fieldNames;
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Take a read through some documentation, such as 'perldoc perlreftut', and the Q&A section here on Perlmonks (Here's a link to the references section).