Experimental Physics and
Industrial Control System

Andrew Johnson via Core-talk <core-talk at aps.anl.gov> · Mon, 08 Jun 2020 22:53:37 -0000

';' was used by the original VxWorks Global Symbol support to terminate
the symbol name to be looked up from later parts of the PV name; it's
still documented as being supported by the current version:
https://github.com/epics-
modules/symb/blob/e44a1f10ae72e56d89fbe22cd8ca8f9e42229304/symbApp/devSymbFind.c#L56

We do have a few records at the APS which have a ';' in their names, and
we were recently discussing using it in the APS-Upgrade naming
convention to introduce optional naming components, to simplify or speed
up parsing, so that usage here may grow.

I have some vague recollection that + has been used for something else
(not here at APS though), but I don't now remember what it was, it might
even have been in one of my training lectures.

In an old tech-talk post there was a suggestion that starting PV names
with a '-' was a bad idea because the caget/caput/camonitor programs
mistake the PV name for a flag. They do support the -- flag though, so I
think that should just be a suggestion, not a hard rule.

In general I would not be in favor of making any name illegal that
follows the documented legal character set; people have asked many times
over the years what characters were allowed in record names and I've
pointed them at the AppDevGuide. If they actually followed that advice I
wouldn't want to break the naming conventions they might have developed.

Using characters that are not in the documented set though opens up
names that might work now to being denied in the future, such as the
braces {}, use of which is now limited by the simple JSON detection in
dbParseLink(). I didn't want to start writing down exactly what all the
rules were when I added JSON support though, so I didn't add them to
that list.

One thing we probably should do though is disallow any characters that
are not strictly 7-bit ASCII. I really don't want to have to check or
enforce UTF-8 rules. Interestingly nobody has ever asked me about i18n
or l10n of strings in EPICS.

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https://bugs.launchpad.net/bugs/1882520

Title:
  Constant arrary input links of size 1 don't work

Status in EPICS Base:
  In Progress

Bug description:
  Constant input links in array form with 1 element don't work and
  return an empty array.

  Example:
  field (INP, [42])

  As soon as a comma is present, it works:
  field (INP, [42,])

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System