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Re: pipe a buffer to a program's stdin using popen

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Kenny McCormack <gazelle@shell.xmission.com> wrote:
> Kaz Kylheku  <480-992-1380@kylheku.com> wrote:
>> John Forkosh <forkosh@panix.com> wrote:
>>> Suppose I have a program that, in part, runs another program
>>> using FILE *outptr=popen("some command string","r") and then
>>> fread()'s its stdout from outptr. Now, if that other program
>>> is otherpgm which reads input from its stdin, and I also want
>>> that input to come from a file inputfile, then I could easily
>>> just write  FILE *outptr=popen("cat inputfile|otherpgm","r");
>>
>>That would be a useless use of cat; it could be done with:
>>
>>  FILE *outptr=popen("otherpgm < inputfile","r");
> 
> Yeah, I noticed that, too.  I think that, in this day and age, we can
> probably ignore it - assume it was there only for pedagogic purposes,
> and that OP actually knows better.

Yup (maybe "illustrative" rather than "pedagogic").

> That said, two observations on the original question:
> 
> 1) This is, of course, completely OT in clc.  People who live their
> lives around keeping clc pure and untainted by OT posts will no doubt
> start jumping up and down about this any post now...

Sorry about that, though I think maybe in stackexchange there'd possibly
be two simultaneously relevant tags: Unix C. I'm obviously interested
in implementing a solution, in C, whereby the C-relevance.

> 2) There are at least a half-dozen possible solutions to OP's problem
> that spring to mind almost immediately.  Which one is best will depend
> on two things:
>  a) How deep OP's problem actually is.  I.e., how much rigor is needed
>     in a solution - i.e., which solution is going to be "good enough".
If it works, it's good enough.

>  b) OP's skill level - and how much grit-and-grime he is willing to put
>     up with.
If it works, I'm probably willing to put up with it.

> That all said, one solution that comes to mind is to use bash's <<<
> operator, like this:
> 
>     sprintf(buffer,"otherpgm <<< '%s'",myinputstring);
>     FILE *outptr=popen(buffer,"r");

Problem is that myinputstring (which is what I called
unsigned char buffer[9999] in original question) can be
many megabytes long, containing lots of hex chars (including \000).
If it were short and ascii, I might have illustratively
alternatively written
     sprintf(buffer,"echo \"%s\" | otherpgm",myinputstring);
along the same lines as our "cat" discussion above.

> Now, the problem with this is that, on most systems,
> things run with popen() don't get bash, even if bash
> is the standard and most commonly used shell on the system.
> Sometimes, they get bash, but invoke it in a way that
> disables most of the bash goodies (e.g., <<<).
> 
> Fixing this is left as an exercise for the reader...
> (It *can* be done, but it gets messy)

-- 
John Forkosh  ( mailto:  j@f.com  where j=john and f=forkosh )

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Thread

pipe a buffer to a program's stdin using popen John Forkosh <forkosh@panix.com> - 2022-01-01 09:35 +0000
  Re: pipe a buffer to a program's stdin using popen Mark Bluemel <mark.bluemel@gmail.com> - 2022-01-01 03:22 -0800
    Re: pipe a buffer to a program's stdin using popen Meredith Montgomery <mmontgomery@levado.to> - 2022-01-01 11:21 -0300
    Re: pipe a buffer to a program's stdin using popen John Forkosh <forkosh@panix.com> - 2022-01-02 09:34 +0000
  Re: pipe a buffer to a program's stdin using popen Kaz Kylheku <480-992-1380@kylheku.com> - 2022-01-01 19:51 +0000
    Re: pipe a buffer to a program's stdin using popen gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-01 21:00 +0000
      Re: pipe a buffer to a program's stdin using popen John Forkosh <forkosh@panix.com> - 2022-01-02 09:12 +0000
    Re: pipe a buffer to a program's stdin using popen John Forkosh <forkosh@panix.com> - 2022-01-02 09:30 +0000
      Re: pipe a buffer to a program's stdin using popen Kaz Kylheku <480-992-1380@kylheku.com> - 2022-01-03 00:03 +0000
        Re: pipe a buffer to a program's stdin using popen John Forkosh <forkosh@panix.com> - 2022-01-03 08:07 +0000
          Re: pipe a buffer to a program's stdin using popen Manfred <noname@add.invalid> - 2022-01-03 22:54 +0100
  Re: pipe a buffer to a program's stdin using popen Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-01 15:00 -0800
    Re: pipe a buffer to a program's stdin using popen gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-02 00:01 +0000
  Re: pipe a buffer to a program's stdin using popen Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2022-01-02 12:54 +0000
    Re: pipe a buffer to a program's stdin using popen gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-02 14:54 +0000
      Re: pipe a buffer to a program's stdin using popen Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2022-01-02 15:37 +0000
      Re: pipe a buffer to a program's stdin using popen John Forkosh <forkosh@panix.com> - 2022-01-02 18:00 +0000
        Re: pipe a buffer to a program's stdin using popen gazelle@shell.xmission.com (Kenny McCormack) - 2022-01-02 18:03 +0000
    Re: pipe a buffer to a program's stdin using popen John Forkosh <forkosh@panix.com> - 2022-01-02 17:51 +0000

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