C: > 的实现不替换文件

Question

我正在为我自己的“shell”在 c 中实现运算符 >。但是，当输入“cat new.txt > new2.txt”时，会发生一些奇怪的事情:

> cat new.txt
This is a file. 
This file contains some text.

> cat new2.txt
This is also afile. 
This file also contains some text.
This file is called new2.txt.

> cat new.txt > new2.txt

> cat new2.txt
This is a file. 
This file contains some text.
me text.
This file is called new2.txt.

有人知道为什么会这样吗？我希望 new2.txt 被删除然后写入。

然后我重定向数据的行是:

...
pipe(pipefd);
pid = fork();
if (pid == 0)
{
  int fd = open(filename[OUT], O_WRONLY | O_CREAT, S_IRUSR | S_IWUSR);
  dup2(fd, STDOUT_FILENO);
  close(fd);
  execvp(par[0], par);
  exit(-1);
}
waitpid(pid, NULL, 0);
close(pipefd[READ]);
close(pipefd[WRITE]);

Answer 1

您在 open 标志中离开了 O_TRUNC。奇怪的是，you're the second person this evening to make that mistake .