What is the meaning and function of 幸 in "则幸分我一杯羹"?
幸 in this context means to hope for.


  吾翁即若翁。必欲烹爾翁，則幸分我一杯羹
  
  My old man is your old man. If you want to boil your old man alive, then I hope that you’ll share a portion of the soup with me.




As far as I can find, the original text says 必欲烹「而」翁 rather than 必欲烹「爾」翁, but the interpretation is the same.