Returns an array containing the elements of the group structure. The array has both numeric indices, each of which is a string naming one member of the group, and named string indices. The array elements are:
$_["name"] string groupname (users)
$_["gid"] integer gidnumber (e.g. 0 for wheel/root)
$_["members"] int number of users in group
$_[0]..$_[n] string usernames in the group