foreach $id (keys %hashes) {
  push @ids, $id if ( cond($hashes{$id}) );
}

sub cond {
  my %line = %{shift};

  return (  (  ($line{'key1'} eq "foo") 
                  and 
                ($line{'key1'} eq "bar")
            )
           or
            ($hashes{$id}{'key4'} < 10)
         );
}