[lsiebert]

It seems that "$" is a special ID for the last message, as opposed to the last possible message.

I would humbly suggest that "^" would be a suitable symbol for the first message in a stream. ^ and $ are used in regex (and vim) in a similar way.

That way you could write "XREAD BLOCK 5000 STREAMS newstream ^" and get all the messages in a stream from the beginning, and then block until a new message comes in all with a single command. You would still be able to add a count if needed, to prevent client flooding.

[antirez]

Exactly, $ is the last message ID, + the greatest, - the smallest. I chose the dollar exactly because of regex assonance. However the corresponding ^ is kinda useless because with XREAD we specify the last ID we got, so it would result in not returning the first element of the stream. It means that it's more useful to specify just 0 in that case.