CIYAWASAY

用pipe()與dup()寫出 ps aux | grep ghhwang | wc > foo 的效果

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

#define READ   0
#define WRITE  1
#define STDIN  0
#define STDOUT 1

int main() {
   int pid_1, pid_2, pid_3, pfd_1[2], pfd_2[2], fd;

   pipe(pfd_1);
   pipe(pfd_2);

   if( (pid_1 = fork()) != 0 ) {
      if( (pid_2 = fork()) != 0 ) {
         if( (pid_3 = fork()) != 0 ) {
            close(pfd_1[READ]);
            close(pfd_1[WRITE]);
            close(pfd_2[READ]);
            close(pfd_2[WRITE]);
            wait((int *)0);
            wait((int *)0);
            wait((int *)0);
         }
         else {
            close(STDIN);
            dup(pfd_2[READ]);
            close(pfd_1[READ]);
            close(pfd_1[WRITE]);
            close(pfd_2[READ]);
            close(pfd_2[WRITE]); 

            fd = open("foo", O_WRONLY | O_CREAT, S_IREAD | S_IWRITE);
            close(STDOUT);
            dup(fd);
            close(fd);

            execl("/bin/wc", "wc", (char *)NULL);
         }
      }
      else {
         close(STDIN);
         close(STDOUT);
         dup(pfd_1[READ]);
         dup(pfd_2[WRITE]);
         close(pfd_1[READ]);
         close(pfd_1[WRITE]);
         close(pfd_2[READ]);
         close(pfd_2[WRITE]);
    
         execl("/bin/grep", "grep", "ghhwang", (char *)NULL);
      }
   }
   else {
      close(STDOUT);
      dup(pfd_1[WRITE]);
      close(pfd_1[READ]);
      close(pfd_1[WRITE]);
      close(pfd_2[READ]);
      close(pfd_2[WRITE]);
   
      execl("/bin/ps", "ps", "aux", (char *)NULL);
   }
   exit(0);
}

# posted by SwanBear @ 12:57