I am building a hash where the keys, associated with scalars, are not necessarily unique. I want the desired behavior to be that if the key is unique, the value is the scalar. If the key is not unique, I want the value to be an array reference of the scalars associated witht the key. Since the hash is built up iteratively, I don't know if the key is unique ahead of time. Right now, I am doing something like this:

if(!defined($hash{$key})){
   $hash{$key} = $val;
}
elseif(ref($hash{$key}) ne 'ARRAY'){
my @a;
push(@a, $hash{$key});
push(@, $val);
$hash{$key} = \@a;
}
else{
push(@{$hash{$key}}, $val);
}

Is there a simpler way to do this?