popen: how to test for end of program

[bastiaannaber]

I am trying to write a program which uses popen but I have a problem. I
want to detect if the program I call with popen has ended. For example:

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main()
{
FILE *pipe = NULL;
int i=0;

while(1) {
if (i == 10) {
pipe = popen("ls", "w");
}

if(pipe != NULL && feof(pipe)) {
printf("Program has ended\n");
}

i++;
usleep(1000);
}
}

This doesn't work.

Does anyone know how to test if the program has ended ?

Thanks,
Bastiaan

[SM Ryan]

ba***********@gmail.com wrote:
# I am trying to write a program which uses popen but I have a problem. I
# want to detect if the program I call with popen has ended. For example:

You don't have that much control with popen/pclose. The available stdout has been
exhausted when you get an EOF; the child has exitted when pclose returns. If you
need finer level control, you have to do the fork(), pipe(), exec*(), and
wait*() calls yourself.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
Who's leading this mob?

[CBFalconer]

ba***********@gmail.com wrote:

I am trying to write a program which uses popen but I have a problem. I
want to detect if the program I call with popen has ended. For example:

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
.... snip ...
Does anyone know how to test if the program has ended ?

Since nothing you mention, apart from <stdio.h>, exists in the
portable standard C language, the answer is NO, nobody here knows.
However, if you were to move to a newsgroup where those things are
topical, possibly with unix in its name, the answer might be
different.

--
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http://www.caliburn.nl/topposting.html
http://www.netmeister.org/news/learn2quote.html

[Jens.Toerring]

ba***********@gmail.com wrote:

I am trying to write a program which uses popen but I have a problem. I
want to detect if the program I call with popen has ended. For example: #include <stdio.h>
#include <sys/types.h>
#include <unistd.h> int main()
{
FILE *pipe = NULL;
int i=0; while(1) {
if (i == 10) {
pipe = popen("ls", "w");
}

if(pipe != NULL && feof(pipe)) {
printf("Program has ended\n");
}

i++;
usleep(1000);
}
} This doesn't work. Does anyone know how to test if the program has ended ?

Probably, but since it's off-topic here in clc most people won't
discuss it here since it's not a C problem - standard C doesn't
know about other programs running at the same time or about func-
tions like popen(). So you better ask these kinds of questions
in a group like comp.unix.programmer, where it's on-topic (but
also there you probably will get told that you hardly can get
that to work with popen() and that you will need to use fork()
and one of the exec()-family of functions - and that you need
"r" as the second argument to popen() when you it with "ls",
ls is supposed to create output for you to read, isn't it?).

But there's also a C related problem with your program: feof()
won't tell you anything reasonable before you actually have read
something from a file. feof() can't predict if EOF will get re-
turned on the next read, it only can tell you afterwards that
this was the reason why a read from the file failed. So, even if
your program spawned by using popen() already died and closed its
side of the pipe, just calling feof() won't help you a bit since
you never read anything, and only that (plus emptying the pipe)
could lead to feof() returning something other than 0.

Regards, Jens
--
\ Jens Thoms Toerring ___ Je***********@physik.fu-berlin.de
\__________________________ http://www.toerring.de

[Alan Balmer]

On Thu, 12 May 2005 15:12:10 -0000, SM Ryan
<wy*****@tango-sierra-oscar-foxtrot-tango.fake.org> wrote:

ba***********@gmail.com wrote:
# I am trying to write a program which uses popen but I have a problem. I
# want to detect if the program I call with popen has ended. For example:

You don't have that much control with popen/pclose. The available stdout has been
exhausted when you get an EOF; the child has exitted when pclose returns. If you
need finer level control, you have to do the fork(), pipe(), exec*(), and
wait*() calls yourself.

Please do the OP the service of directing him to a newsgroup where
this question is topical. You can answer it there, and he can get
input and review from others as well.

--
Al Balmer
Balmer Consulting
re************************@att.net

[SM Ryan]

# Please do the OP the service of directing him to a newsgroup where
# this question is topical. You can answer it there, and he can get
# input and review from others as well.

Maybe Chris can divulge the secret answer.

# From: [e-mail] (Chris Torek)
# Newsgroups: comp.unix.questions,comp.lang.c
# Subject: Re: UNIX commands in C
# Message-ID: <12***@dog.ee.lbl.gov>
# Date: 29 Apr 91 20:15:41 GMT
# References: <19********************@jack.sns.com> <GL*****************@curie.ces.cwru.edu> <17*@shasta.Stanford.EDU>
# Reply-To: [e-mail] (Chris Torek)
# Organization: Lawrence Berkeley Laboratory, Berkeley
# Lines: 21
# X-Local-Date: Mon, 29 Apr 91 13:15:41 PDT
#
# (Having just written a new man page for popen, I cannot resist following
# up, even though I should be off getting some food....)
#
# In article <[e-mail]> [e-mail] (shap) writes:
# >popen(3) also has an interesting "feature." ... Et Voilla! instant deadlock.
#
# This cannot happen directly because of popen(). The reason is
# trivially simple: popen opens either for reading or for writing, never
# both. Thus popen() is unable to create a loop, and deadlock occurs
# only in the presence of a pipe loop. (The situation described in `...'
# is the simplest case, where A writes to B and then reads back from B:
# A->B->A. The problem also occurs in longer loops such as A->B->C->D->A.)
#
# >For those of you who don't believe this happens, talk to some people
# >who have had to port various window managers.
#
# These generally use bidirectional entities such as ptys and must
# therefore provide their own synchronization mechanisms.
# --
# In-Real-Life: Chris Torek, Lawrence Berkeley Lab CSE/EE ([phone])
# Berkeley, CA Domain: [e-mail]

--
SM Ryan http://www.rawbw.com/~wyrmwif/
You face forward, or you face the possibility of shock and damage.

[Alan Balmer]

On Fri, 13 May 2005 14:11:50 -0000, SM Ryan
<wy*****@tango-sierra-oscar-foxtrot-tango.fake.org> wrote:

# Please do the OP the service of directing him to a newsgroup where
# this question is topical. You can answer it there, and he can get
# input and review from others as well.

Maybe Chris can divulge the secret answer.

# From: [e-mail] (Chris Torek)
# Newsgroups: comp.unix.questions,comp.lang.c
# Subject: Re: UNIX commands in C
# Message-ID: <12***@dog.ee.lbl.gov>
# Date: 29 Apr 91 20:15:41 GMT

<remainder snipped>

I have no idea of the intent or relevance of your remark, or the
purpose of quoting a 14 year old, cross-posted message from Chris
Torek.

Please set your mail client to use the conventional quote character.

--
Al Balmer
Balmer Consulting
re************************@att.net

[CBFalconer]

SM Ryan wrote:

# Please do the OP the service of directing him to a newsgroup where
# this question is topical. You can answer it there, and he can get
# input and review from others as well.

Maybe Chris can divulge the secret answer.

PLONK for idiocy, topposting, bad quote marks, general annoyance.

--
Some informative links:
news:news.announce.newusers
http://www.geocities.com/nnqweb/
http://www.catb.org/~esr/faqs/smart-questions.html
http://www.caliburn.nl/topposting.html
http://www.netmeister.org/news/learn2quote.html

[SM Ryan]

CBFalconer <cb********@yahoo.com> wrote:
# PLONK for idiocy, topposting, bad quote marks, general annoyance.

How many times are you going to have plonk before it sticks? You need
to repair your killfile.

[SM Ryan]

Alan Balmer <al******@att.net> wrote:
# On Fri, 13 May 2005 14:11:50 -0000, SM Ryan
# <wy*****@tango-sierra-oscar-foxtrot-tango.fake.org> wrote:
#
# ># Please do the OP the service of directing him to a newsgroup where
# ># this question is topical. You can answer it there, and he can get
# ># input and review from others as well.
# >
# >Maybe Chris can divulge the secret answer.
# >
# ># From: [e-mail] (Chris Torek)
# ># Newsgroups: comp.unix.questions,comp.lang.c
# ># Subject: Re: UNIX commands in C
# ># Message-ID: <12***@dog.ee.lbl.gov>
# ># Date: 29 Apr 91 20:15:41 GMT
# <remainder snipped>
#
# I have no idea of the intent or relevance of your remark, or the

Your pretence of ignorance is amusing. You really don't want to let the
viewers
at home realise the little coup d'etat of comp.lang.c, overthrowing a
once useful
newsgroup, making it the home of a obnoxious clique that is perfectly
willing
to rant (on and on and) on plainly off-topic issues.

# Please set your mail client to use the conventional quote character.

Explain to the new newsgroup the RFC that defined quote characters and
the
importance of using Usenet-approved response formats.

[Keith Thompson]

"SM Ryan" <sm****@acm.org> writes:

Alan Balmer <al******@att.net> wrote: [...] # Please set your mail client to use the conventional quote character.

Explain to the new newsgroup the RFC that defined quote characters and
the
importance of using Usenet-approved response formats.

As far as I know, there is no RFC that specifies what quote character
to use. That's not the point. "> " is the *conventional* prefix.
Your use of "# " causes problems for some of your readers. Your use
of long lines (significantly longer than 72 columns, sometimes longer
than 80 columns) causes even more problems.

For example, I read news in an 80-column window. My newsreader lets
me reformat an article to fit; it even adjusts "> " quoting characters
as it reformats the text. But it doesn't recognize '#' as a quoting
character. Perhaps that's a flaw in my newsreader, but it's an
understandable one, since hardly anybody uses '# as a quoting
character.

I've asked you before why you persist in doing this. I'd ask you
again, but you probably won't answer. I see no benefit to it, unless
you're deliberately trying to annoy people.

BTW, I just noticed that you added a cross-post to alt.usenet.kooks;
I've deleted it.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Mark McIntyre]

On 13 May 2005 23:01:06 -0700, in comp.lang.c , "SM Ryan"
<sm****@acm.org> wrote:

CBFalconer <cb********@yahoo.com> wrote:
# PLONK for idiocy, topposting, bad quote marks, general annoyance.

How many times are you going to have plonk before it sticks? You need
to repair your killfile.

okay, I'll plonk you too, you're being too dang annoying now.
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt>

[CBFalconer]

Mark McIntyre wrote:

"SM Ryan" <sm****@acm.org> wrote:

CBFalconer <cb********@yahoo.com> wrote:

# PLONK for idiocy, topposting, bad quote marks, general annoyance.

How many times are you going to have plonk before it sticks? You
need to repair your killfile.

okay, I'll plonk you too, you're being too dang annoying now.

Well, your quote showed that the PLONK has taken effect properly.
For general information, about once every year or two I clear my
killfile, both to reduce the filtering work and to give reformed
nuisance idiots a chance. Ryan obviously has not reformed.

--
Some informative links:
news:news.announce.newusers
http://www.geocities.com/nnqweb/
http://www.catb.org/~esr/faqs/smart-questions.html
http://www.caliburn.nl/topposting.html
http://www.netmeister.org/news/learn2quote.html

[Keith Thompson]

schlectersamen <un****@fauna.start> writes:
[snip]

Feel free to start screaming any time now.

Please keep this out of comp.lang.c. Thank you.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[CBFalconer]

schlectersamen wrote:

Keith Thompson <ks***@mib.org> wrote in

schlectersamen <un****@fauna.start> writes:
[snip]

Feel free to start screaming any time now.

Please keep this out of comp.lang.c.

Request denied.

PLONK

--
Some informative links:
news:news.announce.newusers
http://www.geocities.com/nnqweb/
http://www.catb.org/~esr/faqs/smart-questions.html
http://www.caliburn.nl/topposting.html
http://www.netmeister.org/news/learn2quote.html

[smryan]

CBFalconer wrote:
# schlectersamen wrote:
# > Keith Thompson <ks***@mib.org> wrote in
# >> schlectersamen <un****@fauna.start> writes:
# >> [snip]
# >>> Feel free to start screaming any time now.
# >>
# >> Please keep this out of comp.lang.c.
# >
# > Request denied.

Now you've done it. You got yourself a really big

# PLONK

all caps and everything. Watch out or next time he'll pull
out the big guns. Like trying to play with the followup-to
header.

[Alan Balmer]

On 13 May 2005 23:34:44 -0700, "SM Ryan" <sm****@acm.org> wrote:

Alan Balmer <al******@att.net> wrote:
# On Fri, 13 May 2005 14:11:50 -0000, SM Ryan
# <wy*****@tango-sierra-oscar-foxtrot-tango.fake.org> wrote:
#
# ># Please do the OP the service of directing him to a newsgroup where
# ># this question is topical. You can answer it there, and he can get
# ># input and review from others as well.
# >
# >Maybe Chris can divulge the secret answer.
# >
# ># From: [e-mail] (Chris Torek)
# ># Newsgroups: comp.unix.questions,comp.lang.c
# ># Subject: Re: UNIX commands in C
# ># Message-ID: <12***@dog.ee.lbl.gov>
# ># Date: 29 Apr 91 20:15:41 GMT
# <remainder snipped>
#
# I have no idea of the intent or relevance of your remark, or the

Your pretence of ignorance is amusing. You really don't want to let the
viewers
at home realise the little coup d'etat of comp.lang.c, overthrowing a
once useful
newsgroup, making it the home of a obnoxious clique that is perfectly
willing
to rant (on and on and) on plainly off-topic issues.

# Please set your mail client to use the conventional quote character.

Explain to the new newsgroup the RFC that defined quote characters and
the
importance of using Usenet-approved response formats.

Bye, now. Have a good life after your recovery.

<Plonk>

--
Al Balmer
Balmer Consulting
re************************@att.net

[Alan Balmer]

On Sat, 14 May 2005 16:22:39 GMT, CBFalconer <cb********@yahoo.com>
wrote:

Mark McIntyre wrote:

"SM Ryan" <sm****@acm.org> wrote:

CBFalconer <cb********@yahoo.com> wrote:

# PLONK for idiocy, topposting, bad quote marks, general annoyance.

How many times are you going to have plonk before it sticks? You
need to repair your killfile.

okay, I'll plonk you too, you're being too dang annoying now.

Well, your quote showed that the PLONK has taken effect properly.
For general information, about once every year or two I clear my
killfile, both to reduce the filtering work and to give reformed
nuisance idiots a chance. Ryan obviously has not reformed.

Apparently, he's afraid to give his advice in a topical newsgroup when
there are other subject experts watching.

--
Al Balmer
Balmer Consulting
re************************@att.net