如何将system()的输出重定向到文件? [英] How to redirect the output of system() to a file?

问题描述

在此C程序

#include <stdio.h>
#include <fcntl.h>
int main()
{
    int file = open("Result", O_CREAT|O_WRONLY, S_IRWXU);

    dup2(stdout, file);
    system("ls -l");

    return 0;
}

我正在尝试将 system()的输出重定向到文件，为此，我使用了 dup2 ，但是它不起作用.

I'm trying to redirect the output of system() to a file, for that i have used dup2 but it is not working.

此代码有什么问题?
并且，请告诉我是否有更好的方法来做到这一点? (不使用终端上的>)

What's wrong with this code?
and, please tell me if there is any better way to do this? (without using > at the terminal )

推荐答案

stdout是标准输出流的FILE *指针. dup2需要文件描述符，您也弄乱了参数顺序. 使用

stdout is a FILE * pointer of the standard output stream. dup2 expects file descriptor, also you've messed up the parameters order. Use

dup2(file, 1);

相反.

关于这部分的更好方法.这种方法很不好，因为您可能要在此system调用完成之后恢复标准输出.您可以通过多种方式执行此操作.您可以在某处dup，然后将其dup2放回原处(并关闭dup ped一个).我个人不喜欢编写其他答案中建议的自己的cat实现.如果您唯一想做的就是将带有system的单个shell命令重定向到文件系统中的文件，那么可能最直接，最简单的方法就是构造shell命令来做到这一点

On the better-way-to-do-this part. This way is bad because you probably want to restore your standard output after this system call completes. You can do this in a variety of ways. You can dup it somewhere and then dup2 it back (and close the dupped one). I personally don't like writing own cat implementations as suggested in other answers. If the only thing you want is redirecting a single shell command with system to a file in the filesystem, then probably the most direct and simple way is to construct the shell command to do this like

system("ls -l > Result");

但是，如果文件名(结果)来自用户输入，则必须小心，因为用户可以提供诸如'Result; rm -rf /*'之类的文件名.

But you have to be careful if filename (Result) comes from user input as user can supply something like 'Result; rm -rf /*' as the filename.

此外，在安全性主题上，您应该考虑按照注释中的建议指定ls的完整路径:

Also, on the topic of security, you should consider specifying the full path to ls as suggested in the comments:

system("/bin/ls -l > Result");

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