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Learn how to efficiently add a new key-value to a specific element in a JSON array using jq, with clear examples and explanations.
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Adding a New Element to an Existing JSON List Element with jq

When working with JSON data, it’s common to need to modify its structure or content. One typical scenario is adding a new element to a specific entry in a list based on a given condition. If you're familiar with the command-line tool jq, this task can become quite straightforward. In this post, we will explore how to efficiently add a new element to an existing JSON list element using jq, equipped with practical examples.

Understanding the Problem

Imagine you have the following JSON structure that defines a "parent" with a "child-list." Each item in this list has a "usecase" property. Here’s how it looks:

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

The Goal

You want to modify the JSON to add a new property, "result": "SUCCESS" to an existing item where usecase is "second." The modified JSON should look like this:

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

The Solution

To achieve this modification using jq, you'll use a specific command that not only selects the relevant element in the list but also updates it with a new key-value pair. Here’s a breakdown of how to do that:

Step-by-step Instructions

Use the |= Operator: The key to success in this operation is using the |= operator instead of just |. The |= operator updates the object instead of merely mapping it.

Map and Select: Use the map() function to iterate over the array, and select() to find the item you want to update.

Add the New Key-Value Pair: Use += to add the new result property to the selected item.

The jq Command

Here’s the command that accomplishes the task:

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

Explanation of the Command

jq - Invokes the jq tool.

'.parent."child-list"' - Navigates to the "child-list" of the parent object.

|= map(...) - Updates the "child-list" using the result of the map() function.

select(.usecase=="second") - Selects the object in the list where the usecase matches "second."

+= { "result": "SUCCESS" } - Adds a new property result to the selected object.

Conclusion

Adding a new element to a list in a JSON structure can efficiently be achieved using jq. Remember to use the |= operator to update your JSON instead of merely passing through the current state. This straightforward command allows you to enhance your JSON data seamlessly, enabling you to tailor your data structure to your specific needs.

By applying this method, you can handle various data manipulation tasks in your projects with ease. Happy coding with jq!