Instead of using the x operator, we could have used the the && operator. The advantage here is that it codes simpler, and the disadvantage is it has no movable parts (since it is not an array).

no strict; no warnings;

my $part = 'http://example.net/app'
           . ($admin           &&  $is_admin_link)
           . (defined $subsite &&  $subsite)
           . $mode
           . (defined $id      &&  $id)
           . (defined $submode &&  $submode)
           ;
print $part;
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