Межпроцессное взаимодействие

#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
 
#define READ 0
#define WRITE 1
 
pid_t open_pipe_to_rw(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 = 0, outfp = 0;
    char buf[128] = "";
 
    if (open_pipe_to_rw("sort", &infp, &outfp) <= 0)
    {
        printf("Unable to exec sort\n");
        exit(1);
    }
 
    write(infp, "4\n", 2);
    write(infp, "3\n", 2);
    write(infp, "2\n", 2);
    write(infp, "1\n", 2);
    close(infp);
 
    read(outfp, buf, 128);
    printf("-------- read ---------\n%s\n", buf);
 
    return 0;
}