running scripts like oracle sqlplus

I have been trying to figure out how I can run a pgsql script like I can run
a plsql script with oracle's sqlplus. Here is a sample script file for what
I want to run:

declare
sysuserid integer := 0;
hwcustid integer := 0;
begin

select nextval( 'user_seq' ) into sysuserid;
select nextval( 'customer_seq' ) into hwcustid;

insert into user
(
user_id,
customer_id,
create_user,
update_user
)
values
(
sysuserid,
hwcustid,
sysuserid,
sysuserid
);

insert into customer
(
customer_id,
create_user,
update_user
)
values
(
hwcustid,
sysuserid,
sysuserid
);

commit;

end;

I try to run the script in psql and thru pgadmin and cannot seem to make
them work. I do not want to turn it into a function. I just want it to
execute the block in a fashion similar to Oracle'sqlplus running
@scriptfile.sql.

Thanks