[JENKINS-47014] Groovy Pipeline Use an assignment within a "while" condition error

I use @​Grab annotation to load Java jar from maven center. Then I wrote java language in my groovy file.  I have some code pieces like the following:

while ((read = fInputStream.read(buffer)) != -1) {

    fOptStream.write(buffer, 0, read);              

}

I read a file and then save to another location, if the file ends, then return -1.

This code works fine on my local groovy 2.4.12. but when I execute the groovy file in Jenkins. I got endless loop in while. I printed the log and found the read value is correct(-1), but it won't break the while loop. It seems that the return value is the result of the assignment. So I modify the code as follows:

read = fInputStream.read(buffer)

while (read != -1) {

    fOptStream.write(buffer, 0, read);    

    read = fInputStream.read(buffer)          

}

It can work normally.

I guess there might be something wrong in Jenkins embedded groovy engine. 

It doesn't support an assignment within a while condition.

---
Originally reported by jackyim, imported from: Groovy Pipeline Use an assignment within a "while" condition error

• assignee: jackyim
  
• status: Reopened
  
• priority: Trivial
  
• component(s): workflow-cps-plugin
  
• resolution: Unresolved
  
• votes: 0
  
• watchers: 2
  
• imported: 2025-12-07
  

Raw content of original issue

I use @Grab annotation to load Java jar from maven center. Then I wrote java language in my groovy file.  I have some code pieces like the following:



while ((read = fInputStream.read(buffer)) != -1) {

    fOptStream.write(buffer, 0, read);              

}





I read a file and then save to another location, if the file ends, then return -1.


This code works fine on my local groovy 2.4.12. but when I execute the groovy file in Jenkins. I got endless loop in while. I printed the log and found the read value is correct(-1), but it won't break the while loop. It seems that the return value is the result of the assignment. So I modify the code as follows:



read = fInputStream.read(buffer)

while (read != -1) {

    fOptStream.write(buffer, 0, read);    

    read = fInputStream.read(buffer)          

}



It can work normally.


I guess there might be something wrong in Jenkins embedded groovy engine. 


It doesn't support an assignment within a while condition.

environment

```
Jenkins version: 2.73.1

Pipeline: Shared Groovy Libraries 2.9
```

Start by reproducing the reported assignment-in-a-while-condition example against workflow-cps-plugin using the stated Jenkins 2.73.1 and Pipeline Shared Groovy Libraries 2.9 environment. Compare its behavior with local Groovy 2.4.12 and verify that end-of-file causes the loop to terminate; the issue does not name a source file or test to update.

Written by the indexing model from the issue text.