Assuming your Perl is at least semi-modern, you can do

use List::Util 'uniq';

my @uniqueOutput = uniq( @output );

List::Util has been in Perl since Perl version 5.7.3, and uniq() has been in List::Util since List::Util 1.45. There are also variants (uniqnum(), etc) should they be more appropriate to your use.