# untested!
my %b;

open(B, "<" . DUMP_B) || die("Could not open file \n");
while (<B>) {
  chomp;
  my ($id, $ac) = split /\|/, $_;
  push @{$b{$id}}, $ac;
}

open(A, "<" . DUMP_A) || die("Could not open file \n");
while(<A>) {
  chomp;
  my $ac = $b{$_} || [];
  print "$_: ", join(', ', @$ac), "\n";
}