COPY equivalent for updates

Is there a COPY equivalent for updates?

eg I've

create table t1 (
id int primary key,
col1 int,
col2 int,
col3 varchar(32)
);

and a CSV file
10,4,5,"abc"
13,7,3,"def"
18,12,77,"ghi"

I'd like to

UPDATE t1 (col1, col2, col3) from file with @1 as primary key;
or
UPDATE t1 (col1, col2, col3) from file where @1=id;

sort of...

Otherwise what is the fastest approach?

I can think of 2 approaches:
1)load a temp table with COPY

update t1 set col1=temp_t1.col1, col2=temp_t1.col2
where t1.id=temp_t1.id;

2) use awk to generate update statements.

Supposing I could neglect the awk execution time, will COPY + UPDATE
be faster than executing a list of UPDATE?

Considering I've to deal with a where clauses anyway... when (and
if) should I create an index on the id of temp_t1?
t1 will contain 700-1M records while I may update a maximum of 20K a
time.

thanks

--
Ivan Sergio Borgonovo
http://www.webthatworks.it