Executing shell script which contains a while loop from Java

Question

I am having a critical trouble to execute a shell script which contains a while loop. Here is my shell script:

echo Here 1
sleep 0.05
echo Here 2
sleep 0.05
echo Here 3

ic=70
while [ $ic -ge 40 ]
do
        #sleep 0.05
        ic=$[$ic-1]
        echo Here $ic
done

When I am executing the script normally from the terminal as /home/pi/tbe/testSleep.sh it is working. and printing all the echos.

Now I have written this java method to execute the file:

public static void main(String[] args) throws IOException, InterruptedException {       
    String command = "/home/pi/tbe/testSleep.sh";
    System.out.println("Executing command: " + command);

    Process process = new ProcessBuilder(command).start();

    BufferedReader reader = new BufferedReader(new InputStreamReader(
            process.getInputStream()));
    String line = null;

    while ((line = reader.readLine()) != null) {
        System.out.println(line);
    }

    process.waitFor();
    int exitValue = process.exitValue();
    System.out.println("Command executed. Exit value: " + exitValue);
    process.destroy();  
}

And when I am executing it I can only see the following output:

Executing command: /home/pi/tbe/testSleep.sh
Here 1
Here 2
Here 3
Here $[70-1]
Command executed. Exit value: 0

This is really weird. Any pointer would be very helpful to me.

Specify the shell you want to use for the shell script. String[] command = {"/bin/bash", "/home/pi/tbe/testSleep.sh"}; Or add shebang in the script itself - #!/bin/bash (as first line). — amit_g
– amit_g, Commented May 13, 2014 at 16:27
You are testing your script using bash. When called from the java process, the script is invoked using sh. The script makes use of features not supported in sh, hence the difference in behavior. — devnull
– devnull, Commented May 13, 2014 at 16:28
It seems that the script is not properly interpreted, as it isn't run by the shell. Have you tried to add #!/bin/bash? — Pablo Lozano
– Pablo Lozano, Commented May 13, 2014 at 16:29
Thank you everybody. The issue is the shebang. I didn't added the #!/bin/bash through I created my process builder as @amit_g suggested. If you can post your comment as an answer I will accept it. Thanks again. — Tapas Bose
– Tapas Bose, Commented May 13, 2014 at 16:43

amit_g · Accepted Answer · 2014-05-13 16:57:48Z

1

It seems that the shell executing the command is not same as that you are using to run the script on command line. Specify the shell as bash.

Add shebang in the script (as first line). It is always a good practice to be specific about the shell in the script

#!/bin/bash

You could also specify the shell you want to use for the shell script

String[] command = {"/bin/bash", "/home/pi/tbe/testSleep.sh"};

answered May 13, 2014 at 16:57

amit_g

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Comments

Steve11235 · Accepted Answer · 2014-05-13 16:32:44Z

1

I ran your script in Ubuntu:

$ sh script.sh
Here 1
Here 2
Here 3
Here $[70-1]
script.sh: 8: [: Illegal number: $[70-1]

Apparently $[70-1] is not being evaluated but simply treated as a literal...

I saw the comments after I saved. They are correct. Using bash (I was lazy) gives the correct results.

answered May 13, 2014 at 16:32

Steve11235

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