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我正在尝试使用 C 实现这个 linux 命令。 ls -l | 剪切-b 1

我试图这样做的方式是

在父进程中调用 ls -l 将 ls -l 的输出放入文件中（写入文件）

在读取文件的子进程中调用剪切（在父进程中写入的文件）将剪切应用于打印输出的文件

到目前为止，这是我所做的

/* pipe.c */
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

void main()
{
   int filedes[2];
   int p;
   pid_t pid, pid1;
   p=pipe(filedes);
   FILE *stream;
   char buff[20];
   
   printf("pipe command returns %d, %d ,%d\n",p, filedes[0],filedes[1]);
   
   if(pipe(filedes) == -1) /* Create the pipe */
      printf("error pipe");
      pid1=fork();
      pid=getpid();
      switch (pid1) { /* Create a child process */
      case -1:
         printf("error fork");
      case 0: /* Child */
      /* Close unused write end */
      /* Child can now read from pipe */
         if (close(filedes[1]) == -1)
            printf("error close");
         printf("I am a child process pid %d, and will read from pipe\n",pid);
         
         while (read(filedes[0], &buff, 1) > 0)
            write(STDOUT_FILENO, &buff, 1);

         write(STDOUT_FILENO, "\n", 1);
         close(filedes[0]);
         _exit(EXIT_SUCCESS);

         break;
         
         default: /* Parent */
         /* Close unused read end */
         /* Parent can now write to pipe */
         if (close(filedes[0]) == -1)
            printf("error close");
         printf("I am the parent process pid %d, and will write to pipe\n", pid );
         stream = fdopen(filedes[1], "w");
         strcpy(buff, "This is a test\n");
         write(filedes[1], buff, strlen(buff));

         char *args[80];
         args[0] = "ls";
         args[1] = "-l";
         args[2] = NULL;
         execvp(args[0],args);
  
         int bak, new;
         bak = dup(1);
         new = open("/home/urwa/abc.txt", O_WRONLY);
         dup2(new, 1);
         close(new);

           

         close(filedes[1]);          /* Reader will see EOF */
         wait(NULL);                /* Wait for child */
         exit(EXIT_SUCCESS);

         break;
   }
}

这段代码工作得很好。并在展台输出测试语句。以及 ls -l 输出。但文件是空的。我究竟做错了什么。我也尝试了如下的 freopen .. 仍然是空文件。：/

 FILE *fp;
 fp = freopen ("/temp/abc.txt", "a+", stdout);
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1 回答 1

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您没有在孩子中调用 cut 并且文件描述符在这里也搞砸了。

为了执行任务，您必须在 execvp 之前关闭父级的标准输出并在父级中使写入结束标准输出。在孩子中，您必须在 execvp 之前关闭孩子的标准输入并以标准输入的形式对您的孩子进行读取。以这种方式（创建管道 b/w 两个）。your parent's stdout is stdin of your child

int main()
{
   int filedes[2];
   int p;
   pid_t pid = 0, pid1 = 0;
   p=pipe(filedes);
   FILE *stream;
   char buff[20];
   char *args[80];

   printf("pipe command returns %d, %d ,%d\n",p, filedes[0],filedes[1]);

   if(pipe(filedes) == -1) /* Create the pipe */
      printf("error pipe");
      pid1=fork();
      pid=getpid();
      switch (pid1) { /* Create a child process */
      case -1:
         printf("error fork"); break;
      case 0: /* Child */
      /* Close unused write end */
      /* Child can now read from pipe */
         if (close(filedes[1]) == -1)
            printf("error close");
         printf("I am a child process pid %d, and will read from pipe\n",pid);

         close(0); //close stdin of child
         dup(filedes[0]); //make pipes read end stdin of child

         args[0] = "cut";
         args[1] = "-b";
         args[2] = "1";
         args[3] = NULL;
         execvp(args[0],args);
         break;

         default: /* Parent */
         /* Close unused read end */
         /* Parent can now write to pipe */
         if (close(filedes[0]) == -1)
            printf("error close");
         printf("I am the parent process pid %d, and will write to pipe\n", pid );

         close(1); //close stdout
         dup(filedes[1]); //make write end of pipe stdout of parent
         args[0] = "ls";
         args[1] = "-l";
         args[2] = NULL;
         execvp(args[0],args);
         break;
   }
}
于 2013-05-07T06:47:24.480 回答