use strict;
my %s;
sub rexists (\%;@) {
  my ($href, @values) = @_;
  for (@values) {
    return 0 unless ref($href);
    return 0 unless exists $href->{$_};
    $href = $href->{$_};
  }
  return 1;
}
print rexists(%s,qw(a b c)),"\n";
$s{a}{b}{c} = 1;
print rexists(%s,qw(a b c)),"\n";