A library used to get groups or members of a netgroup NIS map.
listgroup() without any parameters or listgroups() lists all the
available netgroup groups.

With groupname parameters listgroup, listgroup_user, listgroup_host
will recusively list the members of the named groups. If the groupname
is preceded with a - members of that group will be excluded from the
returned list. Each member in a group is a triplet of
(host,user,domain). The host portion or user portion of the members is
returned by listgroup_host() and listgroup(), the user portion of the
members is returned by listgroup_user().