Using CMD as a Process

Question

I\'m trying to run commands straight through the CMD on Windows (Terminal on Linux). I have the following code. It\'s acting very strangely. First, when run the program does

Answer 1

You can execute commands without actually hard coding cmd.exe into the code.

public static void main(String[] args) {

      //cmd = the command youw ill be using            
    String cmd = "ipconfig";      
    Runtime r = Runtime.getRuntime();      
    Process p;   
    try {       
        p = r.exec(cmd);

    BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));    
    String inputLine;       
    while ((inputLine = in.readLine()) != null) {     
        System.out.println(inputLine);
          }       
    }     


catch (IOException ex) {      
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);  
             }
       }

Answer 2

I found this code on the net years ago. I cant remember where. It's pretty old so there might be something better out there now.

 private void executeCommand(String cmd) {
        try {
            Runtime rt = Runtime.getRuntime();

            Process proc = rt.exec(cmd);

            // any error message?
            StreamHandler errorGobbler = new StreamHandler(proc.getErrorStream(), "ERR");

            // any output?
            StreamHandler outputGobbler = new StreamHandler(proc.getInputStream(), "OUT");

            // kick them off
            errorGobbler.start();
            outputGobbler.start();

            // any error???
            int exitVal = proc.waitFor();
            System.out.println("ExitValue: " + exitVal);
        } catch (Exception e) {
            e.printStackTrace();
        }


    }

And the class:

import java.util.*;
import java.io.*;

public class StreamHandler extends Thread {
    InputStream is;
    String type;
    OutputStream os;

    StringBuffer output;

    StreamHandler(InputStream is, String type) {
        this(is, type, null);
    }

    StreamHandler(InputStream is, String type, OutputStream redirect) {

        this.is = is;
        this.type = type;
        this.os = redirect;
        output = new StringBuffer(100);
    }

    public void run() {
        try {
            PrintWriter pw = null;
            if (os != null)
                pw = new PrintWriter(os);

            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line=null;
            while ( (line = br.readLine()) != null) {
                if (pw != null)
                    pw.println(line);
                System.out.println(type + ">" + line);
            }
            if (pw != null)
                pw.flush();
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
    }
}

Answer 3

Typically cmd or terminal are responsible for setting up standard io for the programs they execute, so I don't think you can just communicate with them via input/output stream. In case of Linux it's actually the shell run inside terminal that executes commands, not terminal itself. Windows probably does some funky things, too.

Answer 4

There could be a couple of things going on. One is that arguments are not getting passed correctly the way you are executing the process. The other, like @zacheusz mentioned, is that output may be coming out from the error stream instead of the input stream.

ProcessBuilder helps with both these things, allowing easy construction of a list of commands and the ability to merge input and error stream. I recommend trying using it:

Process p = null;
try {
    List<String> cmd = new LinkedList<String>();
    cmd.add("executable");
    cmd.add("-arg1");
    cmd.add("value1");
    cmd.add("-arg2");
    ProcessBuilder pb = new ProcessBuilder(cmd);
    pb.redirectErrorStream(true);
    p = pb.start();
    BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
    while (input.ready()) {
        String line = input.readLine();
        System.out.println("From process: "+line);
    }
    input.close();
} catch (IOException e) {
    this.logMessage("IOException caught: "+e.getMessage());
    e.printStackTrace();
}

Answer 5

You need to do this work in a Thread. For example to log the standard output:

Process process = Runtime.getRuntime().exec(command);
LogStreamReader lsr = new LogStreamReader(process.getInputStream());
Thread thread = new Thread(lsr, "LogStreamReader");
thread.start();


public class LogStreamReader implements Runnable {

    private BufferedReader reader;

    public LoggingStreamReader(InputStream is) {
        this.reader = new BufferedReader(new InputStreamReader(is));
    }

    public void run() {
        try {
            String line = reader.readLine();
            while (line != null) {
                System.out.println(line);
                line = reader.readLine();
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Then you need a second thread for input handling. And you might want to deal with stderr just like stdout.

Answer 6

cmd tries to run a command prompt ,

to run the command properly you need the following command line

cmd.exe -c ipconfig.exe

the -c means run the command on the rest of the command line