Interacting with perl through java.

Question

I'm trying to do something with Java that I haven't managed to do until now. I'm trying to interact with a perl process giving him input and reading output.
I have a perl module that has several functions and the idea is to launch a process in a java program with the following line :
perl -e 'while(<STDIN>) { eval $_ ; }'
and then give the process the necessary input and the read the given output.
For instance with the above line you can do the following:
[user@host ~]$ perl -e 'while(<STDIN>) { eval $_ ; }'
print "Hello World\n";
Hello World
Here is the code I'm using:
import java.io.BufferedReader;
public class ExecProgram {
private static Runtime runtime;
private static Process process;
public static void main(String[] args) {
     runtime = Runtime.getRuntime();
     try {
     process = runtime.exec("/usr/bin/perl -e 'while(<STDIN>) { eval $_ ; }'");
          process = runtime.exec(cmd);
     } catch (IOException e) {
          System.err.println("Error executing process");
     PrintWriter out = new PrintWriter(process.getOutputStream());
     String commandLine = "print \"Hello World\n\"";
     out.println(commandLine);
     BufferedReader in = new BufferedReader(new InputStreamReader(process.getInputStream()));
     try {
     String line;
     while ((line = in.readLine()) != null)
          System.out.println("Output: "+line);
     } catch (IOException e) {
     System.err.println("Error reading output");
As you can see I'm using Runtime class to interact with the process but nothing happens if replace the exec line with:
process = runtime.exec("ls");
I can see in the output the listing of the current directory.
Have you ever tried something like this? Is this the correct way for doing this?

Answer 1

Have you ever tried something like this? I have. Here's a rough sample:
    public static void main(String[] args) throws Exception {       
        String[] cmd = new String[]{
            "/usr/bin/perl",
            "-e",
            "while(<>){ eval or die $@; }"
        final Process p = Runtime.getRuntime().exec(cmd);
        new Thread(){
            public void run(){
                try{
                    BufferedReader r = new BufferedReader(new InputStreamReader(p.getInputStream()));
                    for(String line; (line = r.readLine()) != null; System.out.println("ProcessOUT:: "+line));
                catch (Throwable t){
//                    t.printStackTrace();
        }.start();
        new Thread(){
            public void run(){
                try{
                    BufferedReader r = new BufferedReader(new InputStreamReader(p.getErrorStream()));
                    for(String line; (line = r.readLine()) != null; System.err.println("ProcessERR:: "+line));
                catch (Throwable t){
//                    t.printStackTrace();
        }.start();
        new Thread(){
            public void run(){
                try{
                    OutputStream out = p.getOutputStream();
                    for(int ii = 0; ii < commands.length; ii++){
                        System.err.println("Sending command: "+commands[ii]);
                        out.write(commands[ii].getBytes());
                        out.write('\n');
                        out.flush();
                catch (Throwable t){
//                    t.printStackTrace();
        }.start();
        int exit = p.waitFor();
        System.err.println("Process exited with code: "+exit);
    static final String[]
        commands = {
            "print \"The road goes ever\\n\";",
            "print \"ever\\n\";",
            "print \"on.\\n\";",
            "exit 13;"
    ;