#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define READ 0
#define WRITE 1

pid_t
popen2(const char *command, int *infp, int *outfp)
{
    int p_stdin[2], p_stdout[2];
    pid_t pid;

    if (pipe(p_stdin) != 0 || pipe(p_stdout) != 0)
        return -1;

    pid = fork();

    if (pid < 0)
        return pid;
    else if (pid == 0)
    {
        close(p_stdin[WRITE]);
        dup2(p_stdin[READ], READ);
        close(p_stdout[READ]);
        dup2(p_stdout[WRITE], WRITE);

        execl("/bin/sh", "sh", "-c", command, NULL);
        perror("execl");
        exit(1);
    }

    if (infp == NULL)
        close(p_stdin[WRITE]);
    else
        *infp = p_stdin[WRITE];

    if (outfp == NULL)
        close(p_stdout[READ]);
    else
        *outfp = p_stdout[READ];

    return pid;
}

int
main(int argc, char **argv)
{
    int infp, outfp;
    char buf[128];

    if (popen2("sort", &infp, &outfp) <= 0)
    {
        printf("Unable to exec sort\n");
        exit(1);
    }

    write(infp, "Z\n", 2);
    write(infp, "D\n", 2);
    write(infp, "A\n", 2);
    write(infp, "C\n", 2);
    close(infp);

    *buf = '\0';
    read(outfp, buf, 128);

    printf("buf = '%s'\n", buf);

    return 0;
}