Example of how to pipe the stdout of a child process into the parent process and read it into a buffer

stdout-from-child.c

#include <unistd.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <stdio.h>

#define PROCESS "/bin/ls"
#define ARGV "ls", "-la"

void main(void) {
    // fd is the file descriptor for input and output
    // fd[1] is the input side
    // fd[0] is the output side
    int fd[2], nbytes;
    pid_t pid;
    char readbuffer[256];
    
    pipe(fd);
    
    // for if forking fails
    if ((pid = fork()) == -1) {
        perror("fork");
        exit(1);
    }

    if (pid == 0) {
        // child process closes output side of pipe
        close(fd[0]);
        // redirect the child's stdout to the input side; fd[1]
        dup2(fd[1], 1);
	    // execute the child
        execlp(PROCESS, ARGV, NULL);
	    // kill the child
	    exit(0);
    }
    else {
        // wait for child to exit
        waitpid(pid,0,0); 
        // parent process closes input side of pipe
        close(fd[1]);
        // read in the stdout from the pipe
        nbytes = read(fd[0], readbuffer, sizeof(readbuffer));
        // append with terminator
	    readbuffer[nbytes] = '\0';
        printf("Received Start\n%s\nRecived Finish\n", readbuffer);
    }
}