The story that standard output also fatally changes the behavior of the program

I think everyone has the experience of debugging by adding standard output processing (such as ʻecho and System.out.print () `) to scripts and programs that do not work properly. I think that the addition of standard output processing is used in various situations, from simple program operation verification to investigation in an environment where a debugger cannot be used due to restrictions.

However, adding ** 1 line of standard output processing can also fatally change the behavior of the program **.

In the past, the application responded as a result of adding a line of System.out.println (...); to the Java program as a workaround for the problem that the batch stopped due to ** ʻecho`. There were times when I couldn't return **. I would like to explain the memory at that time with Sample Program.

The annual batch has stopped!

About 10 years ago, one day, I received an email from me, who was in charge of maintenance of a certain system, saying, "The annual batch has stopped, so please hurry to investigate." When I read the text further, it says that the program is stopped at the line of the ʻecho instruction in the batch file. ![s1.png](https://qiita-image-store.s3.amazonaws.com/0/43869/914c319b-6923-1178-02d9-55180da8a20d.png) When I first heard it, I doubted the reporter's misunderstanding, but it is true that a batch file containing 4 consecutive lines of ʻecho (Sample here There is k-tamura / stdout-problems / blob / master / src / main / resources / annual.bat)),

・ ・ ・(abridgement)・ ・ ・
echo %date% %time% ==================================================>> logs/result.log
echo %date% %time%  [Step4]                                          >> logs/result.log
echo %date% %time%  Pre-Import Processing                            >> logs/result.log
echo %date% %time%                                                   >> logs/result.log
・ ・ ・(abridgement)・ ・ ・

Looking at the log it output (result.log), I only saw two lines of ʻecho` messages.

・ ・ ・(abridgement)・ ・ ・
2007/09/28 12:04:44.72 ==================================================
2007/09/28 12:04:44.72  [Step4]                                          

(No log has been output since then)

I thought, "That's not possible", but just in case, I decided to build a simple test environment and execute the batch file. The result is as expected. The event was not reproduced and the process was completed normally. I had no idea other than killing the batch process from the outside.

After that, I was able to contact the reporter by phone, so when I heard the details, it was said that this batch was called from a Java program.

The Java program I got from the reporter included the following main () method and started the batch file with java.lang.ProcessBuilder ([Sample here](https: //). github.com/k-tamura/stdout-problems/blob/master/src/main/java/org/t246osslab/stdoutproblems/batch/BatchImpl.java)).

import java.io.*;
import org.springframework.core.io.*;

public class BatchImpl implements BatchInterface {

    public static void main(String[] args) {
        System.out.println("Result: " + new BatchImpl().executeBatch());
    }

    public int executeBatch() {
        try {
            Resource resource = new ClassPathResource("annual.bat");
            File batFile = resource.getFile();
            ProcessBuilder pb = new ProcessBuilder(batFile.getAbsolutePath());
            Process process = pb.start();
            return 0;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return -1;
    }
}

public int executeBatch() {

    //・ ・ ・(abridgement)・ ・ ・

    Process process = pb.start();
    System.out.println(IOUtils.toString(process.getInputStream())); //Add this one line
    return 0;

    //・ ・ ・(abridgement)・ ・ ・
}

@echo off

C:\batch>mkdir logs

C:\batch>echo 2007/09/28 12:04:44.72 ==================================================>> logs/result.log

C:\batch>echo 2007/09/28 12:04:44.73  [Start]                                          >> logs/result.log

C:\batch>echo 2007/09/28 12:04:44.74                                                   >> logs/result.log

C:\batch>echo 2007/09/28 12:04:44.75  Initialize                                      >>logs/result.log

・ ・ ・ (Omitted below) ・ ・ ・