selectecting not null varchars.

I have a table with some text strings and I want to select row where the
text fields have a value in them.

I tried :
select * from directory where length(h) > 0 ;
and got:
ERROR: Null input to textlen

So I tried:
select * from directory where h != null AND length(h) > 0 ;
and got:
ERROR: parser: parse error at or near "and"

In fact this:
select * from directory where h != null ;
... gets you this:
ERROR: parser: parse error at or near ";"

Trying to select where it is equal to null works. Trying to select
where an int is not equal to a certain value works. But I cannot select
where a varchar (or int) is not equal to null.