#ex_16-1
#Learning Perl Appendix A, Exercise 16.1
$: = " ";
while (@pw = getpwent) {
    ($user, $gid, $gcos) = @pw[0,3,6];
    ($real) = split /,/, $gcos;
    $real{$user} = $real;
    $members{$gid} .= " $user";
    ($last) = (split /\s+/, $real)[-1];
    $last{$user} = "\L$last";
}
while (@gr = getgrent) {
    ($gname,$gid,$members) = @gr[0,2,3];
    $members{$gid} .= " $members";
    $gname{$gid} = $gname;
}
for $gid (sort by_gname keys %gname) {
    %all = ();
    for (split(/\s+/, $members{$gid})) {
        $all{$_}++ if length $_;
    }
    @members = ();
    foreach (sort by_last keys %all) {
        push(@members, "$real{$_} ($_)");
    }
    $memberlist = join(", ", @members);
    write;
}
sub by_gname { $gname{$a} cmp $gname{$b}; }
sub by_last { ($last{a} cmp $last{$b}) || ($a cmp $b); }
format STDOUT =
@<<<<<<<< @<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$gname{$gid}, "($gid)", $memberlist
~~                  ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$memberlist
.