COPY use in function with variable file name

Hello,

I can't figure out how to make this work, or is not possible?

In a function i would like to read a file.
The file name is determined by a value from a table.
However the COPY statement does not to accept this?
I tried various forms of adding (single)-quotes but no luck.

Anyone any ideas?

Function:
CREATE FUNCTION dnsdhcp_dns_raw()
/* Fill table dns_raw with dns data */
RETURNS integer AS '
DECLARE   r           RECORD;   ntw         TEXT;
BEGIN   /* Do for all domain names */   FOR r IN SELECT domain FROM network       WHERE position(''n'' IN use) > 0 and
ipaddress!= ''127.0.0.0/24''
 
LOOP       ntw := ''/tmp/db.'' || r.domain;       DELETE FROM dns_raw; /* Clear table */
RAISE NOTICE ''Network: %'', ntw;       COPY dns_raw FROM ntw DELIMITERS ''~''; /* Get the data */   END LOOP;   RETURN
0;
END;'
LANGUAGE 'plpgsql';

Result:
id=# select dnsdhcp_dns_raw();
NOTICE:  Network: /tmp/db.test.dummy.com
ERROR:  parser: parse error at or near "$1"

Tables:
CREATE TABLE dns_raw (   data                TEXT
);
                                 Table "network"    Attribute      |  Type   |                      Modifier
--------------------+---------+---------------------------------------------
-------id                 | integer | not null default
nextval('"network_id_seq"'::text)ipaddress          | cidr    | not nulldomain             | text    | not nullemail
         | text    | not nulllocation           | text    | not null default 'l'use                | text    | not null
default's'ttl                | text    | not null default '3h'serial             | integer | not null default 1refresh
         | text    | not null default '3h'retry              | text    | not null default '1h'expire             | text
  | not null default '1w'cachettl           | text    | not null default '1d'lease_time_default | integer | not null
default86400lease_time_minimum | integer | not null default 0lease_time_maximum | integer | not null default
0client_updates    | text    | not null default 'ignore'ddns_update_style  | text    | not null default
'interim'description       | text    |
 

Best regards,
Roelof