can't pull a string from console with java program

Question

I have the code segment:

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?

Fixed it.

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:

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 SO threads.

Answer 1

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

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:

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

Answer 2

It looks like Java isn't expanding the asterisk:

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:

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;
    }
}