[Dovecot] beginners sieve: copy not move to subfolder?

[voytek at sbt.net.au]

I'm trying to learn how do basic stuff with sieve;

I pasted this from a tutorial, it works fine, mail is delivered to 'friends'

BUT, what should I do to keep mail in main inbasket as well as, copy to
subbasket ?

tried 'copy' but failed so far

main_script: line 6: error: unknown command 'copy' (only reported once at
first occurence).

even after I added 'copy' to 'require' still failed ?

------------------------------------
require ["fileinto", "reject"];

# Daffy Duck is a good friend of mine.
if address :is "from" "daffy.duck at example.com"
{
    fileinto "friends";
}