No intermediate array here.

johngg@aleatico:~$ perl -Mstrict -Mwarnings -E 'say q{};
my $str = q{+book +dog +cat};
say                                   
   join q{, },                                    
   map { q{"} . $_ . q{"} }
   split m{\s+}, $str;'

"+book", "+dog", "+cat"
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I hope this is helpful.