How to list all users in a Linux group?

Question

How do I list all members of a group in Linux (and possibly other unices)?

Answer 1

There is a handy Debian and Ubuntu package called 'members' that provides this functionality:

Description: Shows the members of a group; by default, all members members is the complement of groups: whereas groups shows the groups a specified user belongs to, members shows users belonging to a specified group.

... You can ask for primary members, secondary members, both on one line, each on separate lines.