如何将system（）中命令的stdout传递给self stdin？

Question

Assuming I call something like:

system("ls -1"); // argument minus-one puts one item per line

...how would I capture this in calling process stdin?

From what I've read, system (in Linux) opens a bash-prompt and attempts to execute the command. This indicates the process calling system is parent. Reading about parent process pid suggest this is always 1111 , but I can't find a definite source on this, just linux haxers saying "do this" with neither explanation nor source.

Reading some other sources one can pass data to arbitrary process pipe through /proc/pid/fd/0

Based on reading those, I would think that:

system("ls -1 > /proc/1111/fd/0"); 

...accomplishes this. But it looks like nothing I've done before and my sources for the deduction are not as formal as I'd like them to.

So, is this a portable way of passing output of system command to self stdin?

If not, how would I do it?

Answer 1

It seems you are trying to read the list of all file/folder names in a particular directory. In your case the current working directory. It also appears you are interested in a *NIX solution since you tried to use ls .

There are many ways to read the output from a subprocess into the parent process. You can use fork / exec with pipes or you are use popen .

But for this example you need not go through ls . You are directly read the directory using the Linux API.

You need to use the functions opendir and readdir .

Consider the following program -

#include <sys/types.h>
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>

int main(void) {
    DIR *directory = opendir(".");
    if (directory == NULL)
        return EXIT_FAILURE;
    struct dirent * entry;
    while (entry = readdir(directory)) {
        printf("%s\n", entry->d_name);
    }
    closedir(directory);
    return 0;
}

You might want to skip the "." and ".." entries if you don't want those.

Here is a working demo for the same