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

public class JavaShell {
    public static void main(String[] args) {
        // We use this to start commands
        ProcessBuilder launcher = new ProcessBuilder();
        // Our inherited environment vars.  We may modify these below
        Map<String,String> environment = launcher.environment();
        // Our processes will merge error stream with standard output stream
        launcher.redirectErrorStream(true);
        // Where we read the user's input from
        BufferedReader console =
            new BufferedReader(new InputStreamReader(System.in));

        while(true) {
            try {
                System.out.print("> ");               // display prompt
                System.out.flush();                   // force it to show
                String command = console.readLine();  // Read input

                if (command.equals("exit")) return;   // Exit command

                else if (command.startsWith("cd ")) { // change directory
                    launcher.directory(new File(command.substring(3)));
                }

                else if (command.startsWith("set ")) {// set environment var
                    command = command.substring(4);
                    int pos = command.indexOf('=');
                    String name = command.substring(0,pos).trim();
                    String var = command.substring(pos+1).trim();
                    environment.put(name, var);
                }
                    
                else { // Otherwise it is a process to launch
                    // Break command into individual tokens
                    String[] words = command.split(" ");
                    launcher.command(words);       // Set the command
                    Process p = launcher.start();  // And launch a new process

                    // Now read and display output from the process 
                    // until there is no more output to read
                    BufferedReader output = new BufferedReader(
                             new InputStreamReader(p.getInputStream()));
                    String line;
                    while((line = output.readLine()) != null) 
                        System.out.println(line);
                                     
                    // The process should be done now, but wait to be sure.
                    p.waitFor();
                }
            }
            catch(Exception e) {
                System.out.println(e);
            }
        }
    }
}