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From: =?UTF-8?Q?Arne_Vajh=C3=B8j?= <arne@vajhoej.dk>
Newsgroups: comp.os.vms
Subject: Re: Capturing DCL output in symbol
Date: Tue, 13 May 2025 12:16:42 -0400
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On 5/10/2025 7:40 AM, hb0815 wrote:
> On 5/10/25 03:53, David Meyer wrote:
>> I was wondering if I could use PIPE to do the same thing without having
>> to create and later clean up the temporary file, but so far I have been
>> unable to fine a way to get READ inside a PIPE to set a symbol that's
>> accessible outside the PIPE command.
> 
> Using PIPE: to capture the output of a (DCL) command you need a 
> "pipeline", that is you need "|". For each pipeline you get a sub- 
> processes. Within the sub-process you can assign a DCL symbol with READ. 
> But a symbol in a sub-process is not propagated to the main process. You 
> have to take a detour via a logical name in the job table to get the 
> symbol value into a symbol of the main process.
> 
> $ del/symb t
> %DCL-W-UNDSYM, undefined symbol - check validity and spelling
> $ pipe show time | -
>    (read sys$pipe t ;qt=""""+f$fao("!AS",t)+"""" ;def/job/nolog t &qt) -
>    ;t=f$trnlnm("t")
> $ sh symb t
>    T = "  10-MAY-2025 10:21:19"
> $
> 
> As you can see, the PIPE command contains a sequence of two pipelines 
> and a DCL command. The second pipeline is a subshell. The logical is 
> defined in the sub-process of the second pipeline. The subshell is 
> required or you will not have access to the symbol read by READ. The DCL 
> command runs in your main process. Translating the logical name into a 
> (local) symbol makes its value available in the main process.
> 
> There are limitations. This can only work if the equivalence string of 
> the logical name is valid, does not exceed a limit, etc.
> 
> If your output is a DCL token, then you do not need the quoting (in qt).
> 
> And yes, you need the "&" for the "define". If you use 't' the symbol is 
> evaluated when you enter the command and not when the define is executed.

That is brilliant!

I tried stuffing it in a COM file:

$ vf='f$verify(0)'
$ pipe 'p1' | -
   (read sys$pipe lin ; qlin=""""+lin+"""" ; def/job/nolog res &qlin) ; -
   'p2'==f$trnlnm("res")
$ if vf then exit f$verify(1)+1
$ exit 1

So I can do:

$ @cmd2sym "show time" t
$ sh symb t
   T == "  13-MAY-2025 12:11:57"
$ @cmd2sym "type z.txt" t
$ sh symb t
   T == "A"

Arne