ESP32 Forum

Posted: **Mon Dec 07, 2020 10:25 am**

Hello there,

I am interested in running a pipe of subprocesses written in ANSI C using the ESP32.

The following code is just a sample I have tried to run.

Code: Untitled.c Select all


int parse_output(void) {

    char *cmd = "ls -l";    



    char buf[BUFSIZE];

    FILE *fp;



    if ((fp = popen(cmd, "r")) == NULL) {

        printf("############## Error opening pipe!\n");

        return -1;

    }



    while (fgets(buf, BUFSIZE, fp) != NULL) {

        printf("############## OUTPUT: %s", buf);

    }



    if(pclose(fp))  {

        printf("############## Command not found or exited with error status\n");

        return -1;

    }



    return 0;

}

And the following is the error I receive

Code: Select all

c:\esp\../main/app_main.c:139: undefined reference to `popen`

Is then possible to do it?

Posted: **Mon Dec 07, 2020 6:59 pm**

The code running on the ESP32 is more like the kernel than an Unix-like process. There are no processes, just tasks within a single address space. So I'm not in any way surprised that popen isn't part of the available libraries.

Also, note that popen isn't part of ANSI C (it's probably standardized within POSIX), as it's very much an OS specific function, as opposed to a language / data structure library call.

You should look at FreeRTOS tasks if you want to run something "in parallel" with the existing code. It'll be a function within the SAME program that serves as the thing to run within the other task.

Posted: **Tue Dec 08, 2020 1:29 am**

ESP-IDF indeed does not support the notion of pipes. Suggest you look into using queues or (the ESP-IDF-specific) ringbuffers instead.

Posted: **Mon Dec 14, 2020 7:56 am**

Thanks for your reply.
Considering my intent was changing the ESP32's behavior in run-time, I was able to use the OTA for this purpose.

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