`comm -1 -3` (<a href="http:&#x2F;&#x2F;pubs.opengroup.org&#x2F;onlinepubs&#x2F;9699919799&#x2F;utilities&#x2F;comm.html" rel="nofollow">http:&#x2F;&#x2F;pubs.opengroup.org&#x2F;onlinepubs&#x2F;9699919799&#x2F;utilities&#x2F;co...</a>) is practically made for quickly finding who is a member of all involved groups.