Approved for inclusion in a future ANSI M[UMPS] language standard.
The value of this variable identifies the initial input/output device. The difference between $PRINCIPAL and $PIOREFERENCE is that the value of $PIOREFERENCE always contains a specification of the environment in which the device exists (if the value of $PRINCIPAL is non-empty).
USE $PRINCIPAL WRITE !,$PRINCIPAL,!,$PIOREFERENCE
This document is © Ed de Moel, 1995-2005.
It is part of a book by Ed de Moel that is published under the title "M[UMPS] by Example" (ISBN 0-918118-42-5).
Printed copies of the book are no longer available.
This document describes the various special variables that are defined in the M[UMPS] language standard (ANSI X11.1, ISO 11756).
The information in this document is NOT authoritative
and subject to be modified at any moment.
Please consult the appropriate (draft) language standard for an authoritative definition.
In this document, information is included that will
The MDC cannot guarantee that these 'next' standards will indeed appear.