The variable is
$(user) rather than
$user, so the command would be
!commands add hi hi $(user)
You would need to create separate commands if you wanted Nightbot to respond to other words (hi, hello, hey, etc).
If you wanted something more advanced you could randomize Nightbot’s response with a custom api such as this one: [quote=“rtainc, post:1, topic:4102”]
https://api.rtainc.co/twitch/random?format=I+choose…+&choices=CHOICESReturns a random choice from the parameter. Comma-separated.
(you can find out more about custom api’s here)