Untested:

use List::MoreUtils qw(any);

push @{$vars->{uplinks}}, $conn 
  unless any { $conn eq $_ } @{$vars->{uplinks}};
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Update: After reading sauoq's reply below, I may have misunderstood the question. The OP will have to clarify. If they are saying that if there is *anything* in the array, don't push, but then it would be probably better to get rid of the array entirely as its really not needed.