PL/pgSQL: SELECT INTO only if result count = 1

Hello,

In a PL/pgSQL trigger function, I try to select a record from table
"town" below.

I am only interested in the result if the returned result set contains
exactly one result.
If there is more than one result, I want to log the fact.

EXAMPLE pseudo code

select
country_fk, region_fk, id
from town
where name = 'Newcastle'

if found and count = 1
populate country_id, region_id, town_id
else
raise notice 'ambiguous %', town.name

=======

CREATE TABLE town
(
country_fk character varying(3) NOT NULL,
region_fk character varying(3) NOT NULL,
id serial NOT NULL,
"name" character varying(60) NOT NULL,
CONSTRAINT ...
)
--

Best Regards,
Tarlika Elisabeth Schmitz