Узнай
I have the sentence:
Узнай об этом Саул, он бы убил Самуила.
I am not mistaken, this sentence should be translated as:
If Saul had known about it, he would have killed Samuel.
If my translation is correct, why it seems to me in the first part of the sentence it seems to be using the imperative of the verb узнать. Is it common, or possible with any verb, to construct this type of structure using the imperative?