Скачать или смотреть How to Extract and Enrich Data from JSON in Bash Using jq

Learn how to effectively use Bash pattern matching and `jq` for data extraction and enrichment from JSON files in the command line.
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Extracting and Enriching Data from JSON Using Bash and jq

Working with JSON data in command line environments can often feel cumbersome, especially when trying to extract specific pieces of information based on certain conditions. In this guide, we will explore a solution for a common problem: how to read a JSON file, check for certain patterns in that data, and output specific values in Bash.

The Problem at Hand

Imagine you have a JSON file containing network device information, including connection statuses and timestamps. A sample of this JSON data looks like this:

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You need to iterate over this data, look for specific name entries, check for lastKeepAlive values, and output them accordingly. However, working directly with pure Bash can lead to complications when parsing JSON data.

Simplifying the Solution Using jq

The best way to manage JSON data in Bash is to use a dedicated command-line JSON processor like jq. This tool allows you to easily extract the necessary information without having to write complex parsing logic in Bash.

Step-by-Step Solution

Install jq: If you don't have jq installed, you can usually get it via your package manager. For example, on Debian-based systems, you can install it using:

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Formulate the jq Command:
Instead of implementing a while loop in pure bash, you can directly query the JSON data with jq. This command will help us retrieve the lastKeepAlive values directly from the JSON file:

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In this command:

-r outputs raw strings, not JSON formatted as a string.

select(.name == "PLVM32") filters the items to only those with that specific name.

// "NULL" specifies that if the field does not exist, it outputs "NULL".

Iterate for Different Names:
If you plan to check multiple names, you can wrap the jq query in a loop or call it separately for each name.

Sample Script

Here’s how you could structure a simple Bash script using jq to handle this situation more elegantly:

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Expected Output

When you run the above script, it should print:

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Conclusion

Using jq simplifies the process of extracting and enriching data from JSON files in Bash scripts. By leveraging this tool, you avoid the common pitfalls of JSON parsing in Bash, making your scripts cleaner and more efficient. Don’t hesitate to experiment with different jq commands to suit your needs. Happy scripting!