运行“谁-m” Java命令产生空结果 [英] Running "who -m" command from Java yields empty result

问题描述

我正在尝试从Java查找当前登录的用户名。

I am trying to find the current logged in username from Java.

Process p;
try
{
    p = Runtime.getRuntime().exec("who -m");
    p.waitFor();
    BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));

    String line = "";
    while ((line = reader.readLine()) != null)
        System.out.println(line);
}
catch (Exception e)
{

}

上面的代码不显示任何结果。但是，如果我删除-m选项，它将显示用户名和其他详细信息。而且我还使用-s，-u等其他选项进行了测试。除-m外，所有其他功能均有效。有没有人知道为什么会这样？

The above code does not print any result. However if i remove -m option, it prints user name and other details. And also i tested with other options like -s, -u. It all works except -m. Does anyone has an idea why is it so?

注意：
我知道

Note: I am aware of

System.getProperty("user.name");

但这不是我的解决方案。我正在调用其中使用谁-m的shell脚本。因此，我不能使用Java类。

But that's not a solution in my case. I am calling a shell script in which "who -m" is used. So, I cannot use java classes.

推荐答案

您看到的原因是Java进程启动器不能保证是否存在关联的TTY。在实际的命令行上考虑以下示例：

The reason for what you are seeing is that the Java process launcher does not guarantee the existence of an associated TTY. Consider this example on the actual command line:

$ who -m
user   pts/8        2014-09-02 02:24
$ who -m </dev/null
$

由于标准输入未与第二个 who 呼叫的终端相关联，因此谁无法确定关联的用户。有趣的是，将 stdin 重定向到 / dev / tty 似乎也不起作用：

Since the standard input is not associated with a terminal for the second who call, who cannot determine the associated user. Interestingly enough, redirecting stdin to /dev/tty does not appear to work either:

$ who -m </dev/tty
$

说实话，除非确定与 stdin 相关的用户是准确，否则您应该可能会将您的脚本更新为使用主机名，例如 id -un 或您的解释器可能会提供的其他手段来确定当前用户。

Quite honestly, unless determining the user associated with stdin is exactly what you are after, you should probably update your script to use hostname and e.g. id -un or whatever other means your shell interpretter may offer to determine the current user.

对于那些对细节感兴趣的人，我做了一些挖掘工作，以查找我的另一个答案

For those interested in the details, I did a little bit more digging for another answer of mine.

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