If lan is connected?

I want to write a开发者_如何学运维 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" ?

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You can check : How to detect the physical connected state of a network cable/connector?

I think at least one of the answer should work for you !