As I am mainly a Java guy it has burnt into me to never rely on .toString() output for code flow. It seems to me that this is somewhat similar (or has the Unix world a gentlemans agreement that output has an API contract). I'd never touch anything where I couldn't enforce (preferably typed) output to rely on especially in a security context. I think I have already seen command line tools which can return structured content (json, xml) with a switch (I don't remember which, though).