Скачать или смотреть How to Use jq for Conditional JSON Updates with Environment Variables

Learn how to efficiently use `jq` to convert JSON structures and conditionally update values using environment variables.
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This video is based on the question https://stackoverflow.com/q/77537504/ asked by the user 'Giuliani Sanches' ( https://stackoverflow.com/u/1207665/ ) and on the answer https://stackoverflow.com/a/77537598/ provided by the user 'pmf' ( https://stackoverflow.com/u/2158479/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

Working with JSON data is a common task for developers, especially when dealing with configurations that depend on different environments. A common scenario is needing to replace placeholders in JSON with actual values from environment variables. In this post, we explore how to effectively achieve this using the jq command-line tool, while also troubleshooting common issues that can arise when handling various data types in JSON.

The Problem

Suppose you have a JSON configuration file that includes certain parameters, some of which should be dynamically replaced based on environment variables. For instance, consider the following JSON structure:

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You have set the environment variable ENV_DEFINITION to the value dev. The goal is to convert this JSON into a format where the values are represented as key-value pairs while replacing the environment variable with its actual value. The expected output would be:

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Initial Approach

You managed to obtain the desired output with the following jq command:

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However, complications arose when you needed to include additional parameters that involved numbers:

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Challenges Encountered

Adding these parameters caused the command to fail with the message:

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This happened because jq was trying to access the environment variable using a numeric value, which isn't possible. Subsequently, you experimented with various commands but encountered further issues related to the handling of different JSON types.

The Solution

After some trials, the key insight was to conditionally trigger the variable lookup only for string values. You can utilize select(type == "string") or the shorthand strings. By adjusting your command to replace .[1:] with strings[1:], the command can effectively handle strings while ignoring numbers or other types.

Correct jq Command

Here’s the refined command:

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Breakdown of the Command

.Parameters | to_entries[]: This converts the Parameters object into an array of key-value pairs.

.value |= (env[strings[1:]] // .): This line checks if the value starts with $ and attempts to retrieve its value from the environment, defaulting to the original value if it cannot be found.

join("="): This joins the key and value into the desired format.

Output Validation

When you run the corrected command with your updated JSON file, the output should now accurately reflect the desired configuration with environment variables replaced accordingly:

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Conclusion

Using jq effectively can be quite powerful, especially when dealing with environment-dependent JSON configurations. By understanding the type of data you are working with and leveraging conditional logic, you can create flexible solutions that adapt to varying environments. Feel free to experiment with these concepts and enhance your JSON manipulation capabilities!