When I try that command, it says "unknown command".

Also, I found out that 'write' does not detect duplicates. Any suggestions on an easy way to just compile a list of users that join the stream? And an easy way to compare that list to a user joining the stream?

The only other way I can think of is using writeini, and giving each user a value of "1". (I don't think you can use writeini without a value?)