topic Re: Strange behaviour from DCL PIPE in Operating System - OpenVMS

Strange behaviour from DCL PIPE

Jimson_1 — Tue, 20 Mar 2007 09:43:04 GMT

Hi,

Can anyone explain the following behaviour to me.

1. Create the following command procedure:

$ create a.com
$ write sys$output "This works : _TNA366:" ! use your terminal process name
$ write sys$output "This doesn't work : ''f$getjpi("","TT_PHYDEVNAM")'"

2. Execute it:

$ @a.com
This works : _TNA366:
This doesn't work : _TNA366:

3. Now, try the following PIPE command

$ pipe @a.com | search sys$input TNA366
This works : _TNA366:

Why couldn't it find the second string?

JamesP

Re: Strange behaviour from DCL PIPE

Wim Van den Wyngaert — Tue, 20 Mar 2007 10:03:58 GMT

pipe show proc | type sys$input

Answer : because the process has no terminal.

Wim

Re: Strange behaviour from DCL PIPE

Volker Halle — Tue, 20 Mar 2007 10:12:48 GMT

JamesP,

welcome to the OpenVMS ITRC forum.

Pipes are implemented using sub-processes, which may not have an associated terminal. That's why TT_PHYDEVNAM is returned as an empty string.

Volker.

Re: Strange behaviour from DCL PIPE

Wim Van den Wyngaert — Tue, 20 Mar 2007 10:13:53 GMT

The logical tt is however still pointing to your terminal.

pipe write sys$output f$tr("tt") | type sys$input
FTA14:

Wim

Re: Strange behaviour from DCL PIPE

Jimson_1 — Tue, 20 Mar 2007 10:31:11 GMT

Of course...

Why didn't I think of that?

Cheers guys

Re: Strange behaviour from DCL PIPE

Jan van den Ende — Wed, 21 Mar 2007 03:46:57 GMT

James,

first,
WELCOME to the VMS forum!

please review
http://forums1.itrc.hp.com/service/forums/helptips.do?#33
to thank those that helped

Proost.

Have one on me.

jpe

Re: Strange behaviour from DCL PIPE

Karl Rohwedder — Wed, 21 Mar 2007 04:40:08 GMT

You may make use of the MASTER_PID functin to obtain information of the master process inside the pipe, e.g.

$ write sys$output "This works : _TNA366:" ! use your terminal process name
$ pid = F$Getjpi("","MASTER_PID")
$ write sys$output "This doesn't work : ''f$getjpi(PID,"TT_PHYDEVNAM")'"

regards Kalle

Re: Strange behaviour from DCL PIPE

Jimson_1 — Wed, 21 Mar 2007 06:38:24 GMT

Problem solved.
Thanks