[Info-vax] puzzled by DCL symbol substitution

[Gotfryd Smolik news]

On Sat, 7 Jan 2012, AEF wrote:

> On Jan 7, 12:46 pm, hel... at astro.multiCLOTHESvax.de (Phillip Helbig---
> undress to reply) wrote:
>> <09f5e110-6aa3-44f0-a0bc-d40559d2f... at z1g2000vbx.googlegroups.com>, AEF
>> <spamsink2... at yahoo.com> writes:
>
>>> Back to VMS: Does it say anywhere that COPY NL: filename creates a new
>>> file? And there are some other tricks I can look up as examples.
>>
>> Why would it NOT create a new file?
>
> Where does it say in the user manuals that there even is a creature
> such as NL:?

http://h71000.www7.hp.com/doc/731final/6489/6489pro_038.html
"OpenVMS User's Manual"
[...]
"In the following example, SYS$OUTPUT is defined as a null device (NL:)"

> The only place I've seen it is was in the DCL Dictionary
> for the SPAWN command and it wasn't explained what NL: was.
> All it
> said was "This problem may be avoided by specifying /INPUT=NL:." So if
> you don't know NL: is the null device, how would you even guess to try
> it?

  By mistake, by example ;)

AFAIR, the use of device "trailing shortcut" name (means on the
adapter and port number side, not the alloclass-side) in non-file
structured devices available thru RMS, as long the shortcut is
unique, is also documented somewhere as a general rule, it is only
impossible by example to have a non-template "shortnamed" mailbox
(and much other devices), then rarely (is) useful and used.
  Of course, I don't remember where (it is documented).

  Then NLA0: can be shortened to NLA and NL:

  Having b.ex. TT or TX serial ports you can check:
$ copy/log nla: tta:
%COPY-S-COPIED, NLA: copied to TTA: (0 records)
$
...and if only one TTA0: device exists, the TT logical name
must be removed (with privileges, as it is a /EXEC one)
to check that the "TT:" shortcut also works.

best regards, Gotfryd