error using variable for network device name in 'hook ingress device $external_interface'

[Grant C <grant@xxxxxxx>]

Hello,

Is there special syntax required to use a variable name instead of 
hard-coding the interface name in a declaration like the following?

chain blackhole {
  type filter hook ingress device $external_interface priority -500; 
policy accept

Error: syntax error, unexpected '$', expecting string or quoted string 
or string with a trailing asterisk
                type filter hook ingress device $external_interface 
priority -500; policy accept

using the interface name directly instead of the variable works.

Trying the new syntax that allows using a list, 'ingress devices = { }' 
also fails when using a variable either inside an anonymous list, or as 
the name of a named list.


I am using nftables 9.3 from Debian Buster backports.