How about protocol buffers and content negotiation? Your pipe figures out a proto that program a can emit and program b can consume. ls -> repeated FileDescr

How about protocol buffers and content negotiation? Your pipe figures out a proto that program a can emit and program b can consume. ls -> repeated FileDescriptor files; | repeated string names; Where FileDescriptor is whatever it needs to be, has all the info ls -l does. You have a heirarchy of outputs: if the next takes FileDescriptors, you give it FileDescriptors, if it doesn't you give it strings. What would go to stdout goes through a toString filter.