如何在ruby中比较两个文本文件的值

I have two text file, and they have one same field(pet). I want to combine two file and output a new file contain three fields(owner pet buyer). My code is mainly depends on if both file have the same pet(name and number of pets) than I will add the name of buyer to the field of buyer in the new file. It should print out only if the two file have same filed of pet.I have two text file, and they have one same fi