NetWatch - get IP from host parametr

How to get IP from host parameter of netwatch rule, and use it in “UP|Down” section.

bad example:
/tool netwatch add host=8.8.8.8 up-script=“log warning 8.8.8.8 is UP”

what i want:
/tool netwatch add host=8.8.8.8 up-script=“log warning $host is UP”

any ideas?