@x = map {
  $r = push(@x, $_);
  print(join(",", @x),"\n");
  $r;
} qw(a b c d e);
print join(",", @x), "\n";
__DATA__
a
a,b
a,b,c
a,b,c,d
a,b,c,d,e
1,2,3,4,5