OS system commands

In this chapter you will learn:

1. How to execute a system command
2. How to get and set working directory

Execute a system command

• Process exec(String command)
  Executes the specified string command in a separate process.
• Process exec(String[] cmdarray)
  Executes the specified command and arguments in a separate process.
• Process exec(String[] cmdarray, String[] envp)
  Executes the specified command and arguments in a separate process with the specified environment.
• Process exec(String[] cmdarray, String[] envp, File dir)
  Executes the specified command and arguments in a separate process with the specified environment and working directory.
• Process exec(String command, String[] envp)
  Executes the specified string command in a separate process with the specified environment.
• Process exec(String command, String[] envp, File dir)
  Executes the specified string command in a separate process with the specified environment and working directory.

import java.io.IOException;
//from   ja  va2 s. c  om
public class Main {
  public static void main(String[] args) {
    Runtime runtime = Runtime.getRuntime();

    try {
      Process pro = runtime.exec("notepad.exe");
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

Wait until notepad is terminated.

public class Main {
  public static void main(String args[]) {
    Runtime r = Runtime.getRuntime();/*from ja  va 2  s  . c  om*/
    Process p = null;
    try {
      p = r.exec("notepad");
      p.waitFor();
    } catch (Exception e) {
      System.out.println("Error executing notepad.");
    }
    System.out.println("Notepad returned " + p.exitValue());
  }
}

Get and set working directory

By using the following methods from ProcessBuilder we can get and set working directory when invoking system command.

• File directory()
  Returns this process builder's working directory.
• ProcessBuilder directory(File directory)
  Sets this process builder's working directory.

import java.io.File;
import java.util.Map;
//  j a v  a2s  .c  o  m
public class Main{
  public static void main(String args[]) {

    try {
      ProcessBuilder pb = new ProcessBuilder("myCommand", "myArg1", "myArg2");
      pb.directory(new File("myDir"));
      Process p = pb.start();
    } catch (Exception e) {
      System.out.println("Error executing notepad.");
    }
  }
}

Next chapter...

What you will learn in the next chapter:

1. Get to know the Random class
2. What are the methods available for generating random numbers
3. How random number to shuffle an array

Java standard stream

Java system property get and set

Current time in millis second and nano second

Random UUID

JVM memory

JVM garbage collector

JVM shutting down

Processor count

OS system commands

Random class

Random value

Random value range

Compile Java source code

Timer and TimerTask