Introduction

This is the start of a short series about the JSON data format, and how

the command-line tool jq

can be used to process such data. The plan is to make an open series to

which others may contribute their own experiences using this tool.

The jq command is described on the GitHub page as follows:

jq is a lightweight and flexible command-line JSON processor

…and as:

jq is like sed for JSON data - you can use

it to slice and filter and map and transform structured data with the

same ease that sed, awk, grep and

friends let you play with text.

The jq tool is controlled by a programming language

(also referred to as jq), which is very powerful. This

series will mainly deal with this.

JSON (JavaScript Object

Notation)

To begin we will look at JSON itself. It is defined on

the Wikipedia page

thus:

JSON is an open standard file format and data

interchange format that uses human-readable text to store and transmit

data objects consisting of attribute–value pairs and arrays (or other

serializable values). It is a common data format with diverse uses in

electronic data interchange, including that of web applications with

servers.

The syntax of JSON is defined by RFC 8259 and by

ECMA-404.

It is fairly simple in principle but has some complexity.

JSON’s basic data types are (edited from the Wikipedia page):

Number: a signed decimal number that may contain a

fractional part and may use exponential E notation, but cannot include

non-numbers. (NOTE: Unlike what I said in the audio,

there are two values representing non-numbers: 'nan' and

infinity: 'infinity'.

String: a sequence of zero or more Unicode characters.

Strings are delimited with double quotation marks and support a

backslash escaping syntax.

Boolean: either of the values true or

false

Array: an ordered list of zero or more elements, each of

which may be of any type. Arrays use square bracket notation with

comma-separated elements.

Object: a collection of name–value pairs where the names

(also called keys) are strings. Objects are delimited with curly

brackets and use commas to separate each pair, while within each pair

the colon ':' character separates the key or name from its

value.

null: an empty value, using the word

null

Examples

These are the basic data types listed above (same order):

42

"HPR"

true

["Hacker","Public","Radio"]

{ "firstname": "John", "lastname": "Doe" }

null

jq

From the Wikipedia page:

jq was created by Stephen Dolan, and released in October

2012. It was described as being “like sed for JSON data”. Support for

regular expressions was added in jq version 1.5.

Obtaining jq

This tool is available in most of the Linux repositories. For

example, on Debian and Debian-based releases you can install it

with: