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[ale] C question



Yeah, I've got the standard parent writes to the child process down.  That's not the issue.  I've got to write to one process via a pipe.  That process is not a process I'm writing, but an existing program.  Again, check the example: 

system("echo stuff | somebinary arg1 arg2");

The part I'm wrestling with is the:

echo stuff | somebinary



On Apr 5, 2013, at 7:56 PM, Ed Cashin wrote:

> I was going to write this example before realizing it is probably online, and I found it here:
> 
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/pipe.html
> 
> ... in the docs for standard pipe(2) behavior.  It looks like the stuff after the ellipsis is in main or some other function whose beginning and end aren't shown.
> 
> #include <stdlib.h>
> #include <unistd.h>
> ...
> 
> 
> int fildes[2];
> const int BSIZE = 100;
> char buf[BSIZE];
> ssize_t nbytes;
> int status;
> 
> 
> status = pipe(fildes);
> if (status == -1 ) {
>     /* an error occurred */
>     ...
> }
> 
> 
> switch (fork()) {
> case -1: /* Handle error */
>     break;
> 
> 
> case 0:  /* Child - reads from pipe */
>     close(fildes[1]);                       /* Write end is unused */
>     nbytes = read(fildes[0], buf, BSIZE);   /* Get data from pipe */
>     /* At this point, a further read would see end of file ... */
>     close(fildes[0]);                       /* Finished with pipe */
>     exit(EXIT_SUCCESS);
> 
> 
> default:  /* Parent - writes to pipe */
>     close(fildes[0]);                       /* Read end is unused */
>     write(fildes[1], "Hello world\n", 12);  /* Write data on pipe */
>     close(fildes[1]);                       /* Child will see EOF */
>     exit(EXIT_SUCCESS);
> }
> 
> 
> 
> On Fri, Apr 5, 2013 at 3:33 PM, Geoffrey Myers <lists at serioustechnology.com> wrote:
> So, shaking some cobwebs loose here. How do I replace the following:
> 
> system("echo stuff | somebinary arg1 arg2");
> 
> With a fork/exec ??
> 
> (Digging out my old C books....)
> 
> --
> From my iPhone
> Geoffrey Myers
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> 
> 
> 
> -- 
>   Ed Cashin <ecashin at noserose.net>
>   http://noserose.net/e/
>   http://www.coraid.com/
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--
Until later, Geof



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