12-3

gistfile1.c

#include <signal.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <sys/stat.h>

int main(int argc, char** argv)
{
    close(2);
    int fd[2], fd2[2];
    
    pipe(fd);
    pipe(fd2);

    pid_t pr2 = 0;
    //first process
    if(!(fork()))
    {
        dup2(fd[1], 1);
        close(fd[0]);
        close(fd[1]);
        close(fd2[1]);
        close(fd2[0]);
        execlp(argv[1], argv[1], NULL);
        return -1;
    }
    close(fd[1]);
    //second process started
    if(!(pr2 = fork()))
    {
        dup2(fd2[1], 1);
        dup2(fd[0], 0);
        close(fd[0]);
        close(fd2[1]);
        close(fd2[0]);        
        execlp(argv[2], argv[2], NULL);
        return -1;
    }
    close(fd[0]);
    
    //forth process started
    if(!(fork()))
    {
        dup2(fd2[0], 0);
        close(fd2[1]);
        close(fd2[0]);
        execlp(argv[4], argv[4], NULL);
        return -1;
    }
    close(fd2[0]);
    if(wait(NULL) == pr2)
        wait(NULL);

    if(!(fork()))
    {
        dup2(fd[1], 1);
        close(fd2[1]);
        execlp(argv[3], argv[3], NULL);
        return -1;
    }
    
    close(fd2[1]);
    wait(NULL);
    wait(NULL);
    wait(NULL);
    return 0;
    
}