getgrgid gid
Retrieves a group file (/etc/group) entry by group number gid. The return value in list context is:
where($name, $passwd, $gid, $members)
$members
contains a space-separated list of the login names of the members of the group.
If you want to do this repeatedly, consider caching the data in a hash
using getgrent.
In scalar context, getgrgid returns only the group name.