Open Source For You — December 2017

Developers How To

66 | DECEMBER 2017 | OPEN SOURCE FOR YOU | http://www.OpenSourceForU.com

J

SON has become the most prevalent way of consuming

Web APIs. If you try to find the API documentation of

a popular service, chances are that the API will respond

in JSON format. Many mainstream languages even have

JSON parsers built in. But when it comes to shell scripting,

there is no inbuilt JSON parser, and the only hacker way of

processing JSON is with a combination of awk and sed, which

are very painful to use.

There are many JSON parsers apart from jq but, in this

article, we will focus only on this option.

Installation

jq is a single binary program with no dependencies, so

installation is as simple as downloading the binary from

https://stedolan.github.io/jq/, copying the binary in /bin or

/usr/bin and setting permissions. Many Linux distributions

provide jq in the repositories, so installing jq is as easy as

using the following commands:

sudo apt install jq

...or:

sudo pacman -S jq

Installation instructions may vary depending upon the

distribution. Detailed instructions are available at https://

stedolan.github.io/jq/download/.

This article is a tutorial on using jq as a JSON parser and fetching information

about the weather from different cities.

Usage

For this demonstration, version 1.5 of jq was used. All

the code examples are available at https://github.com/

jatindhankhar/jq-tutorial. jq can be used in conjunction

with other tools like cat and curl, by piping, or be used to

directly read from the file, although the former is more

popular in practice. When working with jq, two fantastic

resources can be used. The first one is the documentation at

https://stedolan.github.io/jq/manual/, and the second is the

Online Playground (https://jqplay.org/) where one can play

with jq and even share the snippets.

Throughout this article, we will use different

API endpoints of the MetaWeather API (https://www.

metaweather.com/api). The simplest use of jq is to pretty

format JSON data.

Let’s fetch the list of cities that contain the word ‘new’ in

them, and then use this information to further fetch details of

a particular city, as follows:

curl -sS https://www.metaweather.com/api/location/

search/?query=new

The above command will fetch all cities containing ‘new’

in their name. At this point, the output is not formatted.

[{“title”:”New York”,”location_type”:”City”,”woeid”:24

59115,”latt_long”:”40.71455,-74.007118”},{“title”:”New

Delhi”,”location_type”:”City”,”woeid”:28743736,”latt_long”

Using jq to Consume

JSON in the Shell