如何在 dup2 中使用 FIFO？

Question

我有 2 個進程，一個從輸入中讀取文件名，然后將該文件名提供給子進程。子進程確定給定文件退出的目錄，子進程將所有目錄名返回給父進程，然后父進程打印這些目錄名稱。我需要使用 FIFO（命名管道）來執行此操作。我將文件名直接放入系統調用以檢查 FIFO 是否可以使用它，但它不起作用，我不知道該怎么做有人請幫忙嗎？

#include <stdio.h>
#include<fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <errno.h>
#include <dirent.h>
//#include <string.h>
extern int errno;

#define FIFO "/tmp/fifo0003.1"
#define FIFO2 "/tmp/fifo0004.1"
int main (void)
{   

int r_fifo, w_fifo, r_fifo2, w_fifo2;
   char filename[100];
   printf("enter filename:");
   scanf("%s",filename);
   char buf[100];
   char buf2[100];
   int fd;
   pid_t pid;
   int stdoutCopy=dup(1);
  if ((mkfifo (FIFO, S_IRUSR | S_IWUSR)) == -1) {
    if(errno == EEXIST)

 perror ("mkfifo()");
 else {
perror("mkfifo()");
    exit (EXIT_FAILURE);
 }   }


if ((mkfifo (FIFO2, S_IRUSR | S_IWUSR)) == -1) {
    if(errno == EEXIST)

 perror ("mkfifo()");
 else {
perror("mkfifo()");
    exit (EXIT_FAILURE);
 }   }

 pid = fork ();
  if (pid == -1)
 {      perror ("fork()");
  exit (EXIT_FAILURE);
}
else if (pid > 0) {
/*parent writes to fifo */
 if ((w_fifo = open (FIFO, O_WRONLY)) < 0) {
 perror ("open()");
 exit (EXIT_FAILURE);      }
 write (w_fifo, filename, strlen (filename));

/*wait for child */
 while (wait (NULL) != pid);
  /*read FIFO2 */
 if ((r_fifo2 = open (FIFO2, O_RDONLY)) < 0) {
 perror ("open()");
 exit (EXIT_FAILURE);      }
//redo stdout
dup2(stdoutCopy,1);
close(stdoutCopy);
read(r_fifo2,buf,strlen(buf));
 buf[strlen(buf)] = '\0';
printf("%s\n",buf);
 else {
     /*child procces */
  if ((r_fifo = open (FIFO, O_RDONLY)) < 0) {
 perror ("open()");
 exit (EXIT_FAILURE);      }
 /*read FIFO */
   read (r_fifo, filename, strlen (filename));
 if ((w_fifo2 = open (FIFO2, O_WRONLY)) < 0) {
 perror ("open()");
 exit (EXIT_FAILURE);      }

  dup2(w_fifo2,1);
  system("find -name file1>w_fifo2");
  close(w_fifo2);
   /* EOF */
 exit (EXIT_SUCCESS);}
 return EXIT_SUCCESS;}

Answer 1

外殼命令

find -name file1>w_fifo2

將標准 output 重定向到名為w_fifo2的文件。

If you want the output of the command to be written to your pipe, represented by the w_fifo2 descriptor in your code, then you should duplicate it into STDOUT_FILENO just like you do now, but not redirect output in the command you run:

find -name file1

---

另請記住，某些find實現需要路徑作為第一個參數，否則命令將失敗：

find . -name file1

談到失敗，你真的應該檢查system返回什么來檢查失敗。 如果你想讓 output 寫入標准錯誤（這是錯誤報告和輸出的正常通道），你還需要用你的 pipe 替換它：

dup2(w_fifo2, STDERR_FILENO);