How to get information about "dhcp-option DNS" from client script?

[ogogon]

Colleagues, tell me, please, how can I get information about "dhcp-option DNS" from a script on the client?

The client runs on a small router, and when connecting and disconnecting OpenVPN, I need to switch the direction of DNS requests to a server in a private network or a server at the provider.
How can I get this information from a shell script?

Thanks in advance,
Ogogon.