lab5_os

#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
int main(int argc, char* argv[]) {
        int fdp1[2];
        int fdp2[2];
        int fdp3[2];
        int fdp4[2];
        int fdp5[2];
        pipe(fdp1);
        pipe(fdp2);
        pipe(fdp3);
        pipe(fdp4);
        pipe(fdp5);
        if(argc < 2) {
                write(1, "Usage: popular file-name words-number\n", 38);
                exit(0);
        }
        if(fork() == 0) {  //  1
                close(1); dup(fdp1[1]); close(fdp1[1]); close(fdp1[0]);
                execl("/bin/cat", "cat", argv[1], (char*) 0);
                exit(1);
        }
        if(fork() == 0) {  //  2
                close(0); dup(fdp1[0]); close(fdp1[0]); close(fdp1[1]);
                close(1); dup(fdp2[1]); close(fdp2[1]);
                execl("/usr/bin/tr", "tr", "-cs", "A-Za-z", "\n", (char*) 0);
                exit(2);
        }
        if(fork() == 0) {  //  3
                close(0); dup(fdp2[0]); close(fdp2[0]); close(fdp2[1]);
                close(fdp1[0]); close(fdp1[1]);
                close(1); dup(fdp3[1]); close(fdp3[1]); close(fdp3[0]);
                execl("/usr/bin/tr", "tr", "A-Z", "a-z", (char*) 0);
                exit(3);
        }
        if(fork() == 0) {  //  4
                close(0); dup(fdp3[0]); close(fdp3[0]); close(fdp3[1]);
                close(fdp1[0]); close(fdp1[1]);
                close(fdp2[0]); close(fdp2[1]);
                close(1); dup(fdp4[1]); close(fdp4[1]);
                execl("/usr/bin/uniq", "uniq", "-i", (char*) 0);
                exit(4);
        }
        if(fork() == 0) {  //  5
                close(0); dup(fdp4[0]); close(fdp4[0]); close(fdp4[1]);
                close(fdp1[0]); close(fdp1[1]);
                close(fdp2[0]); close(fdp2[1]);
                close(fdp3[0]); close(fdp3[1]);
                execl("/usr/bin/sort", "sort", "-u", (char*) 0);
                exit(5);
        }
        if(fork() == 0) {
          close(0); dup(fdp5[0]); close(fdp5[0]); close(fdp5[1]);
          close(fdp1[0]); close(fdp1[1]);
          close(fdp2[0]); close(fdp2[1]);
          close(fdp3[0]); close(fdp3[1]);
          close(fdp4[0]); close(fdp4[1]);
          execl("/usr/bin/tail", "tail", "-l", argv[2], (char*) 0);
          exit(6);
        }
        close(fdp1[0]); close(fdp1[1]);
        close(fdp2[0]); close(fdp2[1]);
        close(fdp3[0]); close(fdp3[1]);
        close(fdp4[0]); close(fdp4[1]);
        close(fdp5[0]); close(fdp5[1]);
        while(wait(0) != (-1));
        exit(0);
}