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Learn how to effectively `reassign parameters` in Jenkins pipeline scripts, overcoming common pitfalls with clear, actionable steps and examples.
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This video is based on the question https://stackoverflow.com/q/68969660/ asked by the user 'Chandan Naik' ( https://stackoverflow.com/u/6280116/ ) and on the answer https://stackoverflow.com/a/68972399/ provided by the user 'Matthew Schuchard' ( https://stackoverflow.com/u/5343387/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering Jenkins: How to Reassign Parameters in a Pipeline Script

If you're diving into the world of Jenkins and Groovy scripting, you might have encountered the need to reassign parameters in your pipeline. This common requirement can become frustrating when you discover that the parameters behave differently than you might expect. In this guide, we’ll explore how to properly handle parameters in a Jenkins Pipeline script and reassign them successfully.

Understanding the Issue

Jenkins pipelines utilize the params object to handle parameters passed to the job. While it may seem intuitive to reassign those parameters directly, the params object does not support variable reassignment after they have been declared. This limitation can lead to runtime errors, particularly the dreaded java.lang.UnsupportedOperationException.

A Quick Look at Your Attempts

In your code, you tried to reassign parameter B to the value of parameter A. Below is the original code you used:

[[See Video to Reveal this Text or Code Snippet]]

However, as you've likely discovered, this leads to an error because params is immutable. The alternative you considered was creating a temporary variable, which while functional, may not be the most elegant solution.

The Proper Way to Reassign Parameters

To work around the immutability issue with params, you'll need to create a new map object to hold your reassigned parameter values. This can be done neatly with Groovy syntax. Here's how you can achieve that:

Step-by-Step Solution

Declare a New Map: Create an empty map that will store the new parameters.

Copy Values: Assign values from the original params to your new map.

Reassign as Necessary: Modify or use the new map in your pipeline logic.

Implementation Example

Here’s a revised version of your function that implements the above steps:

[[See Video to Reveal this Text or Code Snippet]]

Key Takeaways:

Immutability: Remember that params cannot be modified after they are initialized.

Use New Maps: Always create a new map object if you need to modify values that come from the parameters.

Debugging: Employing echo statements can help confirm the parameter values you are working with during the pipeline execution.

Conclusion

By understanding the limitations of the params object within Jenkins and using a new map for reassignment, you can effectively manage parameter values. This ensures your Jenkins pipeline runs smoothly without encountering the unsupported operation errors.

Thank you for following along as we explored how to reassign parameters in a Jenkins pipeline script. Happy scripting!