[ale] C question

[Geoffrey Myers]

I had tried something like that before.  Still didnt work. Turns out, the program must be looking at the real uid as it returns a 'not authorized error'. Thanks for the assistance. 

--
From my iPhone
Geoffrey Myers

On Apr 7, 2013, at 7:40 PM, David Tomaschik <david at systemoverlord.com> wrote:

> set up a pipe, fork(), dup2(pipe_output, STDIN); exec(), (from parent process) push "stuff" into pipe should work for that.
> 
> Something like:
> (Please add error checking...)
> 
> pid_t child;
> int pipefd[2];
> char stuff[] = "stuff";
> 
> pipe(pipefd);
> if((child = fork()) == 0) {
>   // Child
>   dup2(pipefd[0], STDIN_FILENO);
>   execl("/bin/foo", "/bin/foo", "--some-arg");
> }
> write(pipefd[1], stuff, strlen(stuff));
> waitpid(child, ...);
> 
> (Haven't tested it, but this should work...)
> 
> 
> 
> 
> On Sun, Apr 7, 2013 at 4:03 PM, Geoffrey Myers <lists at serioustechnology.com> wrote:
>> 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
>>>> _______________________________________________
>>>> Ale mailing list
>>>> Ale at ale.org
>>>> http://mail.ale.org/mailman/listinfo/ale
>>>> See JOBS, ANNOUNCE and SCHOOLS lists at
>>>> http://mail.ale.org/mailman/listinfo
>>> 
>>> 
>>> 
>>> -- 
>>>   Ed Cashin <ecashin at noserose.net>
>>>   http://noserose.net/e/
>>>   http://www.coraid.com/
>>> _______________________________________________
>>> Ale mailing list
>>> Ale at ale.org
>>> http://mail.ale.org/mailman/listinfo/ale
>>> See JOBS, ANNOUNCE and SCHOOLS lists at
>>> http://mail.ale.org/mailman/listinfo
>> 
>> --
>> Until later, Geof
>> 
>> 
>> 
>> 
>> _______________________________________________
>> Ale mailing list
>> Ale at ale.org
>> http://mail.ale.org/mailman/listinfo/ale
>> See JOBS, ANNOUNCE and SCHOOLS lists at
>> http://mail.ale.org/mailman/listinfo
> 
> 
> 
> -- 
> David Tomaschik
> OpenPGP: 0x5DEA789B
> http://systemoverlord.com
> david at systemoverlord.com
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://mail.ale.org/mailman/listinfo/ale
> See JOBS, ANNOUNCE and SCHOOLS lists at
> http://mail.ale.org/mailman/listinfo
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.ale.org/pipermail/ale/attachments/20130408/94d8bc20/attachment.html>