Parsing JSON in Linux/Mac: A Comprehensive Guide

Last Updated on :December 7, 2024

jq is a lightweight and powerful command-line tool that simplifies JSON parsing. It provides a rich set of features for querying, filtering, and transforming JSON data. 

Using jq to parse JSON:

Suppose you have a JSON file named data.json:

{
   "name": "Rakesh Kumar",
   "age": 35,
   "city": "Bangalore"
}

You can extract the value of a specific key as follows:

cat data.json | jq '.name'

This will extract and print the values of the name, age, and city keys from the JSON file

cat data/data.json | jq '.name, .age, .city'

If your JSON contains arrays, you can access elements by their index. For example:

data.json

{
   "name": "Rakesh Kumar",
    "details" : {
           "age": 35,
           "city": "Bangalore"
    },
    "friends" : ["John", "Jane", "Alice", "Bob"] 
}

To extract the first element of friends array:

cat data.json | jq '.friends[0]'

Nested JSON:

For nested JSON objects, you can access keys using the dot notation. 

Suppose data.json is :

{
   "name": "Rakesh Kumar",
    "details" : {
           "age": 35,
           "city": "Bangalore"
    }
} 

You can extract nested values like this:

cat data.json | jq '.details.age'

Using jq to parse API Response:

Parsing an API response with jq involves fetching the data using a tool like curl and then piping the output to jq for processing. Here’s a step-by-step example:

curl -s http://localhost:3000/employees
Response - 
[
  {
    "id": "1",
    "name": "John Doe",
    "email": "[email protected]",
    "department": "Engineering"
  },
  {
    "id": "2",
    "name": "Jane Smith",
    "email": "[email protected]",
    "department": "Marketing"
  },
 ...

Parse and format the response with jq

curl -s http://localhost:3000/employees | jq -r '.[] | "Name: \(.name)\nEmail: \(.email)\nDepartment: \(.department)"'

This will output:

Name: John Doe
Email: [email protected]
Department: Engineering
Name: Jane Smith
Email: [email protected]
Department: Marketing
...

Parsing JSON in a Shell Script:

You can integrate jq commands into a shell script. Below is an example script that reads a JSON file and prints a specific value:

 employee_arr.json

{
   "employees": [
       {
           "id": "1",
           "name": "John",
           "email": "[email protected]",
           "department": "Engineering"
         },
         {
           "id": "2",
           "name": "Jane",
           "email": "[email protected]",
           "department": "Marketing"
         },
….
      ]
 }

#!/bin/bash
#
# SCRIPT: json_parser.sh
# AUTHOR: Rakesh Panigrahi
# PURPOSE: Script that parses JSON data


# echo "Printing Array Of Employess---------------------------------"
# Parse JSON using jq
employees=$(jq '.employees' data/employee_arr.json)

# Iterate over each employee
for employee in $(echo "${employees}" | jq -c '.[]'); do
   name=$(echo "$employee" | jq -r '.name')
   email=$(echo "$employee" | jq -r '.email')
   department=$(echo "$employee" | jq -r '.department')
   echo "Name: $name, Email: $email, Department: $department"
done

By using jq, you can efficiently parse and manipulate JSON data within your shell scripts on a Linux system.