Pipe of Subprocess in ANSI C

[lcarnevale]

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: [Select all] [Expand/Collapse]

1. int parse_output(void) {
2.     char *cmd = "ls -l";    
3.  
4.     char buf[BUFSIZE];
5.     FILE *fp;
6.  
7.     if ((fp = popen(cmd, "r")) == NULL) {
8.         printf("############## Error opening pipe!\n");
9.         return -1;
10.     }
11.  
12.     while (fgets(buf, BUFSIZE, fp) != NULL) {
13.         printf("############## OUTPUT: %s", buf);
14.     }
15.  
16.     if(pclose(fp))  {
17.         printf("############## Command not found or exited with error status\n");
18.         return -1;
19.     }
20.  
21.     return 0;
22. }

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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?

[davidzuhn]

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.

[ESP_Sprite]

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

[lcarnevale]

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.