A.15 Chapter 16, System Database Access

1. Here's one way to do that:

   $: = " ";
   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
   .

   Yes, this one needs some explaining.