Java program opens command prompt and inserts command

This article uses various approaches for selecting the commands inserted in the opened command window through the Java code. The command window is opened by using ‘cmd’. Here, the methods of doing the same are specified using Java code. The Command window is first opened using the Java program. It is opened as a child process. If the java program is run in an existing cmd window, another one is opened as a new process. Further, different types of commands are inserted and executed in that opened command window via Java code.

These programs may not run in online programming environments. Details on how to run these programs using javac and java commands are detailed in the output section of this article.

algorithm

• Step 1 − Open the CMD window using Java code.

• Step 2 − Select the command to be executed. The selected command is used as a text String.

• Step 3 - Execute the selected command in the open CMD window through the Java program.

• Step 4 − Check the results.

Multiple methods

For these programs, command selection is accomplished through two different methods.

• By Using Commands that change the property of the cmd window.

• By Using Executable Commands

Let’s see the program along with its output one by one.

First, the java code is given to start the new CMD window.

Java Code (to start the new CMD window)

public class cmdprog1 {
   public static void main(String[] args) {
      System.out.println("Opening cmd window");
      try{

         // cmd is a command that opens the command window
         //CMD /C is used to run commands and then terminate the existing window while CMD /K will run the command and then it returns you to the given prompt. Runtime.getRuntime().exec(new String[] {"cmd", "/K", "Start"});
         // the following line can also be used.....
         //Runtime.getRuntime().exec(new String[] {"cmd", "/C", "Start"});
      }
      catch (Exception e){
         System.out.println("Error: " + e);
      }
   }
}

Output

C:\java\javaprgstu>javac cmdprog1.java
C:\java\javaprgstu>java cmdprog1
Opening cmd window
C:\java\javaprgstu>

Method 1: By using the command to change the cmd window properties.

In this approach, two different examples are used.

• Example 1: Change title when opening CMD window.

• Example 2: Change the background and foreground colors when opening the CMD window.

Example 1: Change title when opening CMD window.

Program

public class cmdprog22 {
   public static void main(String[] args) {
      String command_to_playwith =" title 'The New Title of the New Command Window' ";
      System.out.println("Opening cmd window");
      try {
         String command = "cmd /c" + " start" + command_to_playwith;
         //Starting the new child process
         Process childprocess11 = Runtime.getRuntime().exec(command);
         System.out.println("The child process is Alive: " + childprocess11.isAlive());
         System.out.println();
      }
      catch (Exception e){
         System.out.println("Error: " + e);
      }
   }
}

Output

C:\java\javaprgstu>javac cmdprog22.java
C:\java\javaprgstu>java cmdprog22
Opening cmd window
The child process is Alive: true

Example 2: Changes the background and foreground color of the CMD window while opening it.

public class cmdprog55 {
   public static void main(String[] args) {
      
      //the following command will change the color of the cmd window. First the number for bg color and then the number for fg color is added.
      // 4 means red color and 0 means black color
      String command_to_playwith =" COLOR 40";
      System.out.println("Opening cmd window");
      try {
         String command = "cmd /c" + " start" + command_to_playwith;
         
         // starting the child process ....
         Process childprocess11 = Runtime.getRuntime().exec(command);
         System.out.println("The child process is Alive: " + childprocess11.isAlive());
         System.out.println();
      }
      catch (Exception e){
         System.out.println("Error: " + e);
      }
   }
}

Output (Approach 1: Example 2)

C:\java\javaprgstu>javac cmdprog55.java
C:\java\javaprgstu>java cmdprog55
Opening cmd window
The child process is Alive: true

Approach-2: By Using the executable commands

A new cmd window is opened as a child process. The inserted command results can only be seen in a new cmd window. In this approach, three different examples are used.

Example 1: Display message in the open CMD window.

Example 2 Show the contents of a txt file.

Example 3: Display folder contents in wide format.

Example 1: Display message in the open CMD window.

public class cmdprog44 {
   public static void main(String[] args) {
      
      // The following command will display the message specified.
      String command_to_playwith =" ECHO 'Hi! Lets check the cmd commands ....'";
      System.out.println("Opening cmd window");
      try {
         String command = "cmd /c" + " start" + command_to_playwith;
         // starting the child process....
         Process childprocess11 = Runtime.getRuntime().exec(command);
         System.out.println("The child process is Alive: " + childprocess11.isAlive());
         System.out.println();
      }
      catch (Exception e){
         System.out.println("Error: " + e);
      }
   }
}
System.out.println("Opening cmd window");
   try {
      String command = "cmd /c" + " start" + command_to_playwith;
      // starting the child process ....
      Process childprocess11 = Runtime.getRuntime().exec(command);
      System.out.println("The child process is Alive: " + childprocess11.isAlive());
      System.out.println();
   }
   catch (Exception e){
      System.out.println("Error: " + e);
   }

Output (Approach 2: Example 1)

C:\java\javaprgstu>javac cmdprog44.java
C:\java\javaprgstu>java cmdprog44
Opening cmd window
The child process is Alive: true

Example 2: Display the contents of txt file.

public class cmdprog33 {
   public static void main(String[] args) {
      
      //The following command is the command that is needed to see the contents of the given text file
      String command_to_playwith =" TYPE testfile.txt";
      System.out.println("Opening cmd window");
      try {
         String command = "cmd /c" + " start" + command_to_playwith;
         
         //Starting the new child process
         Process childprocess11 = Runtime.getRuntime().exec(command);
         System.out.println("The child process is Alive: " + childprocess11.isAlive());
         System.out.println(" Now showing the content of testfile.txt ....\n");
      }
      catch (Exception e){
         System.out.println("Error: " + e);
      }
   }
}

Output

C:\java\javaprgstu>javac cmdprog33.java
C:\java\javaprgstu>java cmdprog33
Opening cmd window
The child process is Alive: true
Now showing the content of testfile.txt ...

Example 3: Display folder contents in wide format.

public class cmdprog66 {
   public static void main(String[] args) {
      
      // The following command will display the specified directory in wide format
      String command_to_playwith =" dir .\applettest /W";
      System.out.println("Opening cmd window");
      try {
         String command = "cmd /c" + " start" + command_to_playwith;
         
         //Starting the new child process
         Process childprocess11 = Runtime.getRuntime().exec(command);
         System.out.println("The child process is Alive: " + childprocess11.isAlive());
         System.out.println(" Now showing the directory in wide format ....\n");
      }
      catch (Exception e){
         System.out.println("Error: " + e);
      }
   }
}

Output

C:\java\javaprgstu>javac cmdprog66.java
C:\java\javaprgstu>java cmdprog66
Opening cmd window
The child process is Alive: true
Now showing the directory in wide format ...

Conclusion

In this article, we explored different commands to be inserted into the cmd window after opening it through the java program. The selection of commands is done based on the different categories. The first set of commands changes the properties of the command window while opening it and the second set of commands is used to show results in the opened command window after it is displayed. In both cases, the new cmd window is opened as a child process.

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