How to run infinte loop shell script from a java program

Question

I want to run a shell script from a java program. My shell script(loop_shell.sh) is working fine when I am running it in terminal and even my Java program(Execute.java) is working fine while running with other commands like 'ls' etc. But when I try run shell script from the Java program, shell script is not printing the values which are inside a loop. Here are the codes for both shell script and Java Program respectively.

loop_shell.sh:-

 #bin/sh

i=0

j=0

timer=0;

echo "u r in loop_shell.sh"

while((i!=1));

do

 echo "waiting for the folder" 

done

Execute.java:-

import java.io.BufferedReader;

   import java.io.IOException;

   import java.io.InputStream;

   import java.io.InputStreamReader;

   import java.io.File;



   public class Execute
   {

    public static void main (String args[])
    {

     String command="./loop_shell.sh";

     String output=executeCommand1(command);

     System.out.println(output);
    }
        public static String executeCommand1(String command) {

            StringBuffer output = new StringBuffer();

            Process p;

            try {
                File dir = new File("/home/vamz/Desktop/sudhir_personal/JAVA_IMPORTANT/");//path
                p = Runtime.getRuntime().exec(command,null,dir);
                p.waitFor();
                BufferedReader reader = 
                            new BufferedReader(new InputStreamReader(p.getInputStream()));

                            String line = "";           
                while ((line = reader.readLine())!= null) {
                output.append(line + "\n");
                }

            } catch (Exception e) {
        e.printStackTrace();
        }

    return output.toString();

    }

  }

Output:- u r in loop_shell.sh

Expected Output:-

 u r in loop_shell.sh
 u r in loop_shell.sh
 u r in loop_shell.sh
 u r in loop_shell.sh
 u r in loop_shell.sh
 u r in loop_shell.sh
 ..........so on ....

If u try to run both the programs u will get the same output. U can see that output is just printing "u r in loop_shell.sh" and qutting with out waiting for shell script to complete!! Can some one pls explain me what is happening ? and pls tell me how to run infinte loop script from a java program.

Answer 1

After searching in internet and scratching my head for long time I have found out the correct way to run a infinite looped shell script from a java program. MY java program has to be like this:-

import java.io.BufferedReader;

   import java.io.IOException;

   import java.io.InputStream;

   import java.io.InputStreamReader;

   import java.io.File;



   public class Execute
   {

    public static void main (String args[])
    {

     String command="/bin/bash loop_shell.sh"; ----> change in shell command!

     String output=executeCommand1(command);

     System.out.println(output);
    }
        public static String executeCommand1(String command) {

            StringBuffer output = new StringBuffer();

            Process p;

            try {
                File dir = new File("/home/vamz/Desktop/sudhir_personal/JAVA_IMPORTANT/");//path
                p = Runtime.getRuntime().exec(command,null,dir);
                p.waitFor();
                BufferedReader reader = 
                            new BufferedReader(new InputStreamReader(p.getInputStream()));

                            String line = "";           
                while ((line = reader.readLine())!= null) {
                output.append(line + "\n");
                }

            } catch (Exception e) {
        e.printStackTrace();
        }

    return output.toString();

    }

  }

As u can see the bash command has to be like this "/bin/bash/ loop_shell.sh" .Now my java program is waiting for the shell script to complete!!

Answer 2

It is an infinite loop, and you are calling a "p.waitFor()" that waits till the command has finished. That is the problem, just let the script finish and you will see the result.

change the script to:

i=0

j=0

timer=0;

 echo "u r in loop_shell.sh"

while((i!=10));

do

    echo "waiting for the folder" 
    let i=i+1
done