I am not sure if I understood your question correctly but if you are asking how to generate the effect of hitting a return by input pipes, here it is in two different ways:
1.
create a file with a single carriage return character in it (vi myfile, then hit return all by itself and save it)
you can cat this file and pipe it to your script and when the question is asked, it will read the return character from the input pipe
2.
in the script, where it will give you this prompt, you can echo "^M" character to the command (vi the script and create the ^M character by hitting ctrl-V then ctrl-M)
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UNIX because I majored in cryptology...
