vfork-execve.c

#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#include <poll.h>

void test_exec_fork()
{
    pid_t pid;
    int status;
    int out_pipe[2];
    int err_pipe[2];

    if (pipe(out_pipe) || pipe(err_pipe)) {
        perror("ERROR: pipe()");
        return;
    }

    pid = vfork();

    if (pid == 0) {
        close(out_pipe[0]);
        close(err_pipe[0]);

        // while loop because of posible signal interrupt
        while ((dup2(out_pipe[1], STDOUT_FILENO) == -1) && (errno == EINTR)) {}
        while ((dup2(err_pipe[1], STDERR_FILENO) == -1) && (errno == EINTR)) {}

        close(out_pipe[1]);
        close(err_pipe[1]);        

        char *command = "ping -c 5 localhost";
        char *argv[] = { "sh", "-c", command, NULL };
        execve("/bin/sh", argv, NULL);
        perror("execve() failure");
        _exit(1);
    }

    if(pid < 0) {
        perror("vfork() failure");
        return;
    }

    close(out_pipe[1]);
    close(err_pipe[1]);

    printf("Forked PID: %d, waiting...\n", pid);
    
    char buffer[1024];
    struct pollfd plist[] = { { out_pipe[0], POLLIN }, { err_pipe[0], POLLIN } };
    while (1) {
        if (poll(plist, 2, -1) < 0) {
            perror("fork failure!");
            break;
        }

        if (plist[0].revents & POLLIN) {
            int n = read(out_pipe[0], buffer, sizeof(buffer)-1);
            buffer[n] = 0;
            printf(">OUT> %s", buffer);
        }
        else if (plist[1].revents & POLLIN) {
            int n = read(err_pipe[0], buffer, sizeof(buffer)-1);
            buffer[n] = 0;
            printf(">ERR> %s", buffer);
        }
        else {
            break;
        }
    }

    close(out_pipe[0]);
    close(err_pipe[0]);

    pid_t rpid = waitpid(pid, &status, 0);
    printf("Done: %d: %d\n", rpid, status);
}