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Re: 'system': bug or misunderstanding?

From: clerke
Subject: Re: 'system': bug or misunderstanding?
Date: Sat, 5 Jan 2008 02:05:49 +0400
User-agent: KMail/1.9.7

On Friday 04 January 2008 22:29:01 John W. Eaton wrote:
> On  1-Jan-2008, clerke wrote:
> | Shouldn't these two commands both send 'foo' back to my screen?
> | (Octave 3.0.0 on gentoo/amd64, but I noticed it in earlier Octave
> | versions too).
> |
> | octave:1> system ("echo foo; exit 2",1,"async")
> | ans =  829
> | octave:2> foo
> |
> | octave:2> system ("echo foo; exit 2",1,"sync")
> | ans =  2
> | octave:3>
> | octave:3>
> |
> | In particular, i would have thought the sync version should do it.
> No, the sync version should return the output from the system command
> (you specified that with the second argument of 1):

ok, I see now that 'return_output' means to redirect stdout to the second 
output variable. If that's not there (as in my tests above) it just gets lost 
in the sync case.

I'll see if I can make sense of it with some experimentation. 

>   octave:1> [status, output] = system ("echo foo; exit 2",1,"sync")
>   status =  2
>   output = foo
> This is documented, though I suppose not very clearly.  I would
> welcome a patch that improved the doc string.

I'll see if I can come up with some useful patches after some experimentation 
with system and edit.

> | i totally misunderstanding how system should work?
> | And either way, how do I get 'edit' to work?
> If your problem is with edit, then how about sending a precise recipe
> for duplicating the problem your are having with it?

Thought I already did.
i type 'edit foo' at the octave prompt, and the prompt doesn't return. 
However, 'ctrl-x' (the normal way to exit nano) makes the octave prompt 
Nano actually started (and i could probably edit blindly), but I don't see the 
screen display from it. This seemed to be something to do with the way edit.m 
uses system as above, but now I'm not so sure because ...

I have a new bit of information now: when I set the editor to vim, i get a 
message saying 'Vim: Warning: Output is not to a terminal', and it behaves as 
for nano.
I get this message (and the same behaviour) whether I work in kdevelop, 
koctave, konsole terminal emulator, or even a basic console tty.
It's starting to sound like 'not our problem', i guess, but I *can* get vim to 
work outside octave with no trouble.

Is 'edit' even designed to work with these screen editors, or is it only for 
line editors?

> jwe


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