I have
:global eruWAN ether1
/ip firewall filter add chain=forward out-interface=!($eruWAN) ....
which the CLI doesn't like. Nor
/ip firewall filter add chain=forward out-interface=!$eruWAN ....
/ip firewall filter add chain=forward out-interface=(!$eruWAN) returns "Script Error: cannot logically negate string" which makes sense, but
/ip firewall filter add chain=forward out-interface=!ether1 .... works.
How can I use the variable $eruWAN there?