How To Create A Srting From What's Written To The Brower?

In my code, I include a file which writes to the browser. I'm looking for a way to create a string that will contain what the file I included wrote to the browser. For example, the included file (meow.asp): Code:

<% meow = 6 %>
this is a test. the number is: <%= meow+4 %>
<% response.write "hello world!" %>

And my code: Code:

...
<!--#include file="meow.asp"-->
...

I want that somehow I'll have a string in my code that contains: Code:

this is a test. the number is: 10
hello world!

How do I do that?