If lan is connected?

Question

I want to write a script and put it in /etc/rc.local so that

if lan is connected then

rfkill block all

else

nmcli con up id 'Network id' --nowait

How should I write the if part and how should I check for "lan is connected" ?

Answer 1

If the LAN is up, then you'll have a default route; otherwise, you shouldn't. So rather than check for particular interfaces, I'd just check for a default route.

I don't have a Linux box to test on, so can't tell what ip(8) gives you, but route(8) has rather poor error exit codes when there's no routes, so instead I'd just rely upon the exit code of grep -- if there's an interface: line, then you have a LAN.

function have_lan() {
  route -n get  default | fgrep -q interface:
}