不能用java程序从控制台中拉出一个字符串

I have the code segment:

我有代码段：

public static void getOS() throws IOException, InterruptedException
   {
       String[] cmd = {"cat", "/etc/*-release"};
       Process proc = rt.exec(cmd);
       VerboseMode.verboseOut(cmd,proc);

       BufferedReader is = new BufferedReader(new InputStreamReader(proc.getInputStream()));
       line = is.readLine();
       OS = line.trim();
   }

in a program that used to work, but stopped for some reason. If I run cat /etc/*-release from terminal I get results, but from java I get null. What is missing?

曾经工作的程序，但由于某种原因停止了。如果我运行cat / etc / * - 从终端发布我得到结果，但是从java我得到null。什么不见了？

Fixed it.

修复。

I removed the verbose mode line which was directing the output to console instead of the line variable, and changed the format of the cmd string:

我删除了详细模式行，它将输出定向到控制台而不是行变量，并更改了cmd字符串的格式：

public static void getOS() throws IOException, InterruptedException
   {
       String[] cmd = {"/bin/sh","-c","cat /etc/*-release" };
       Process proc = rt.exec(cmd);

       BufferedReader is = new BufferedReader(new InputStreamReader(proc.getInputStream()));
       line = is.readLine();
       OS = line.trim();
   }

I must have changed it and forgot. But for my own info, whats the difference between the two cmd strings shown above, as well as if I passed it in as just a string vs. string[]. It's my understanding that a string may not always work, but a string[] will. but the /bin/sh -c part I'm not sure about, just saw it online before in other S.O. threads.

我必须改变它并忘了。但是对于我自己的信息，我看到上面显示的两个cmd字符串之间的区别，以及我是否仅将其作为字符串与字符串[]传递。我的理解是字符串可能并不总是有效，但字符串[]会有效。但/ bin / sh -c部分我不确定，只是在其他S.O.之前在网上看过它。线程。

2 个解决方案

#1

Inside String you can provide your script which is you are running through terminal

在字符串内，您可以提供正在通过终端运行的脚本

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Multipleprocess {

public static void main(String[] args)throws Exception {
int process=0;
String s[]={"/bin/sh","-c","cat /etc/*-release" };
Process p=Runtime.getRuntime().exec(s);
BufferedReader proc=new BufferedReader(new InputStreamReader(p.getErrorStream()));
BufferedReader pout=new BufferedReader(new InputStreamReader(p.getInputStream()));
// We read stderror first from String because it spits the progress information 
//into   stderr

for (String s1=proc.readLine(); s1!=null; s1=proc.readLine())
{
process++;
System.out.println("Stderr from p: "+s);
}
for (String s1=pout.readLine(); s1!=null; s1=pout.readLine())       
{
process++;
System.out.println("Stdout from p: "+s);
}

//how many process have completed check here 
System.out.println("process have completed"+process);
// if you need to check whether the command actually returned normally

int returnCode = p.waitFor();
proc.close();
pout.close();

System.out.println("Process exited with return code "+returnCode);
}
}

I have checked my programme it running on my eclipse, you can use my programme,I got output like this:

我检查了我在eclipse上运行的程序，你可以使用我的程序，我输出如下：

Stderr from p: [Ljava.lang.String;@186d4c1
Stderr from p: [Ljava.lang.String;@186d4c1
Stderr from p: [Ljava.lang.String;@186d4c1
Stderr from p: [Ljava.lang.String;@186d4c1
process have completed16

Process exited with return code 0 You can see here process completed 16

流程退出并返回代码0您可以在此处看到流程已完成16

#2

It looks like Java isn't expanding the asterisk:

看起来Java没有扩展星号：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class GetOS {
    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println(getFirstLine("/etc/*-release"));
        System.out.println(getFirstLine("/etc/os-release"));
    }

    public static String getFirstLine(String file) throws InterruptedException, IOException {
        ProcessBuilder b = new ProcessBuilder();
        b.command("cat", file);
        Process proc = b.start();
        proc.waitFor();
        System.out.println(proc.exitValue());

        BufferedReader is = new BufferedReader(new InputStreamReader(proc.getInputStream()));
        return is.readLine();
    }
}

If you wanted to expand it yourself, you could use something similar to:

如果你想自己扩展它，你可以使用类似的东西：

import java.io.IOException;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

public class ExpandGlob {
    public static void main(String[] args) throws IOException {
        System.out.println(expandGlob("/etc/*-release"));
    }

    public static List<Path> expandGlob(String pattern) throws IOException {
        Path p = Paths.get(pattern);
        Path dir = p.getParent();

        List<Path> files = new ArrayList<>();
        try (DirectoryStream<Path> s = Files.newDirectoryStream(dir, p.getFileName().toString())) {
            for (Path f : s) {
                files.add(f);
            }
        }
        return files;
    }
}

#1