How do I assign a value to a property name result returned from command line app

[oneilt]

I have a command line app that encrypts and decrypts text. How can i incorporate this into nanat so i can use this command line app to decrypt text and assign the result to a propery value. so far i have the below exec command but im not sure how to assign it to a property value.
 
<exec program="A4CDecrypt" failonerror="false" commandline=""${propsFromEnvSettings}"" />