Recipe help needed

Hi, Every:

I try to write a simple recipe:

When an email arrive in the form:

subject: 12345
message: This is a test

I need to write a recipe that:
1. take the subject line as a variable, say $subject=12345
2. Save the message body to a file, say: test.txt
3. Run a shell command: 

runshod $subject test.txt


Can anyone show me to write such a recipe?

Thanks in advance.

Regards,

Zhenhua