如何在c ++中获取linux命令输出字符串和输出状态

I want to get a Linux command's output string as well as command output status in a C++ program. I am executing Linux commands in my application.

我想在C ++程序中获取Linux命令的输出字符串以及命令输出状态。我在我的应用程序中执行Linux命令。

for example: Command:

例如:命令:

rmdir abcd

Command output string:

命令输出字符串:

rmdir: failed to remove `abcd': No such file or directory

rmdir:无法删除`abcd':没有这样的文件或目录

Command Status:

1 (Which means command has been failed)

1(表示命令失败)

I tried using Linux function system() which gives the output status, and function popen() which gives me output string of a command, but neither function gives me both the output string and output status of a Linux command.

我尝试使用Linux函数system()给出输出状态,函数popen()给出了命令的输出字符串,但这两个函数都没有给我输出字符串和Linux命令的输出状态。

5 个解决方案

#1

The output string is in standard output or standard error descriptor (1 or 2, respectively).

输出字符串是标准输出或标准错误描述符(分别为1或2)。

You have to redirect these streams (take a look at dup and dup2 function) to a place, where you can read them (for example - a POSIX pipe).

您必须将这些流(请参阅dup和dup2函数)重定向到可以读取它们的位置(例如 - POSIX管道)。

In C I'd do something like this:

在C中我会做这样的事情:

int pd[2];
int retValue;
char buffer[MAXBUF] = {0};
pipe(pd);
dup2(pd[1],1);
retValue = system("your command");
read(pd[0], buffer, MAXBUF);

Now, you have (a part of) your output in buffer and the return code in retValue.

现在,您有缓冲区输出(的一部分)和retValue中的返回代码。

Alternatively, you can use a function from exec (i.e. execve) and get the return value with wait or waitpid.

或者,您可以使用exec中的函数(即execve)并使用wait或waitpid获取返回值。

Update: this will redirect only standard output. To redirect standard error, use dup2(pd[1],1).

更新:这将仅重定向标准输出。要重定向标准错误,请使用dup2(pd [1],1)。

#2

The simplest solution is to use system, and to redirect standard out and standard error to a temporarly file, which you can delete later.

最简单的解决方案是使用系统,并将标准输出和标准错误重定向到临时文件,以后可以删除。

#3

Unfortunately there's no easy and simple way in C on Linux to do this. Here's an example how to read/write stdout/stderr/stdin of child process correctly.

不幸的是,在Linux上的C中没有简单易行的方法来做到这一点。这是一个如何正确读取/写入子进程的stdout / stderr / stdin的示例。

And when you want to receive exit code you have to use waitpid (complete example is provided on the bottom of the provided page):

当你想要接收退出代码时,你必须使用waitpid(提供的页面底部提供了完整的示例):

endID = waitpid(childID, &status, WNOHANG|WUNTRACED);

Now you just have to join those two together :)

现在你只需加入这两个:)

There's also a great free book named Advanced Linux Programming (ALP) containing detailed information about these kinds of problem available here.

还有一本名为Advanced Linux Programming(ALP)的免费书籍,其中包含有关此类问题的详细信息。

#4

Building on Piotr Zierhoffer answer above, here's a function that does just that, and also restores stdout and stderr their original state.

在上面的Piotr Zierhoffer回答的基础上,这里有一个功能就是这样,并且还恢复了stdout和stderr的原始状态。

// Execute command <cmd>, put its output (stdout and stderr) in <output>,
// and return its status
int exec_command(string& cmd, string& output) {
    // Save original stdout and stderr to enable restoring
    int org_stdout = dup(1);
    int org_stderr = dup(2);

    int pd[2];
    pipe(pd);

    // Make the read-end of the pipe non blocking, so if the command being
    // executed has no output the read() call won't get stuck
    int flags = fcntl(pd[0], F_GETFL);
    flags |= O_NONBLOCK;

    if(fcntl(pd[0], F_SETFL, flags) == -1) {
        throw string("fcntl() failed");
    }

    // Redirect stdout and stderr to the write-end of the pipe
    dup2(pd[1], 1);
    dup2(pd[1], 2);
    int status = system(cmd.c_str());
    int buf_size = 1000;
    char buf[buf_size];

    // Read from read-end of the pipe
    long num_bytes = read(pd[0], buf, buf_size);

    if(num_bytes > 0) {
        output.clear();
        output.append(buf, num_bytes);
    }

    // Restore stdout and stderr and release the org* descriptors
    dup2(org_stdout, 1);
    dup2(org_stderr, 2);
    close(org_stdout);
    close(org_stderr);

    return status;
}

#5

you can use popen system call, it will redirect output to a file and from file you can redirect output to a string. like :

你可以使用popen系统调用,它会将输出重定向到一个文件,你可以从文件中将输出重定向到一个字符串。喜欢 :

    char buffer[MAXBUF] = {0};
    FILE *fd = popen("openssl version -v", "r");
    if (NULL == fd)
    {
        printf("Error in popen");
        return;
    }
    fread(buffer, MAXBUF, 1, fd);
    printf("%s",buffer);

    pclose(fd);

For more information read man page for popen.

有关更多信息,请阅读popen的手册页。

#1