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

The following shell script will iterate through all users and print only those user names which belong to a given group:

#!/usr/bin/env bash
getent passwd | while IFS=: read name trash
do
    groups $name 2>/dev/null | cut -f2 -d: | grep -i -q -w "$1" && echo $name
done
true

Usage example:

./script 'DOMAIN+Group Name'

Note: This solution will check NIS and LDAP for users and groups (not only passwd and group files). It will also take into account users not added to a group but having group set as primary group.

Edit: Added fix for rare scenario where user does not belong to group with the same name.

Edit: written in the form of a shell script; added true to exit with 0 status as suggested by @Max Chernyak aka hakunin; discarded stderr in order to skip those occasional groups: cannot find name for group ID xxxxxx.