Here's an example of what eduardo may have meant by suggesting you be more specific. Walking through what you wrote, you can see many questions are raised:

I need to match certain lines from a file

1. Do you have the file already? Do you need help on opening it?
2. What kind of matching do you need to do? Are you asking for a regex for a specific problem, or are you asking for a general solution, such as 'you can accomplish this with a regex'?

and print the corresponding arrays

1. What corresponding arrays? You were talking about matching lines...where do the arrays come from?

on other file

1. Again, have you got this part taken care of, or do you need help with opening the file and outputting to it?

In addition to clarifications of the problem, seeing the code in question, the error messages you're getting, and a summary of what you've attempted will help someone trying to offer a solution.

As you can see, it's very difficult for us to answer when you don't provide information about your problem--thus it is not a simple question to answer. It's good that you were able to find your answer because I don't think anyone could help you without more clarification. This node may give you suggestions on how to create a question. If you post any code, you'll also want to look at Site How To, where there's a section on submitting Code and Escaping Characters.

Remember, all we know of your problem and context is what you tell us, so be specific.