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gistfile1.txt

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

int main(int argc, char** argv)
{
    int fd[2], status;
    int f;

    pipe(fd);
    
    if(fork())
    {
        f = open(argv[4], O_RDONLY);

        if(fork()) {
            dup2(fd[1], 1);
            close(fd[0]);
            close(fd[1]);
            execlp(argv[1], argv[1], NULL);
            return -1; 
        }
        else {
            wait(&status);
            dup2(fd[1], 1);
            dup2(f, 0);
            close(fd[0]);
            close(fd[1]);
            execlp(argv[2], argv[2], NULL);
            close(f);
            return -1;
        }
    }
    else {
        f = open(argv[6], O_WRONLY);
        dup2(fd[0], 0);
        dup2(f, 1);
        close(fd[0]);
        close(fd[1]);
        execlp(argv[3], argv[3], argv[5], NULL);
        close(f);
        return -1;
    }
    while(wait(&status) != -1)
        ;
    return 0;
}