Furthermore, I assume you want to track the clicked button's link, so you're firing your Rule with a Click event for that button.
If your button is a stylized <A> link, then one of the "this"'s properties is "href", which would be the button's link. So in Adobe Launch, in your Adobe Analytics Set Variables action, you can configure your eVar like so (my example uses eVar3):
eVar3 Set as %this.href%
This ensures that your eVar always tracks whatever link your clicked button has.