[SOLVED] How to answer a command from the Terminal in Java

Issue

I want to execute a command from Java but this command wants me to give it a username.

Like this example:

$ my command

[command] Username:_

So how can I give the command my username in Java?

Currently my code is like this:

    Process p = Runtime.getRuntime().exec(command);
    BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
    String s;
    while ((s = br.readLine()) != null){
        System.out.println(s);
    }
    br.close();
    p.waitFor();
    p.destroy();

Solution

You need to create another thread and pump user input through process#getOutputStream(). See the following example:

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

public class ProcessWithInput {

    public static void main(String[] args) throws IOException, InterruptedException {
        Process p = Runtime.getRuntime().exec("cat");
        OutputStream os = p.getOutputStream();
        os.write("Hello World".getBytes());
        os.close();
        BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String s;
        while ((s = br.readLine()) != null) {
            System.out.println(s);
        }
        br.close();
        p.waitFor();
        p.destroy();
    }
}

Ofcourse, you need to do proper error/exception handling etc.

Other option is to use ProcessBuilder which allows you to provide input through a File.

Answered By - Dakshinamurthy Karra