JG

A CLI tool to generate JSON from the command-line.

Motivation

In my day to day work, I find myself using the excellent httpie tool to test REST apis I'm working on.

Usually, those APIs accept and produce JSON payloads. httpie comes with handy support for generating the JSON body of outgoing requests.

However, this support is pretty basic and suffers from several limitations:

• The generated JSON is only one level deep (httpie/cli#78)
• Bare bone support for arrays

Out of frustration with these issues, I ended up writing jg to solve them.

At a glance

jg is run from the command-line with one or multiple generator expressions describing the desired JSON:

jg 'customer = { id=:33 name=jawher address.zip=123 links.repos=[:1 :2 :3]}'

This produces the following JSON

{
       	"customer": {
       		"id": 33,
       		"name": "jawher",
       		"address": {
       			"zip": "123"
       		},
       		"links": {
       			"repos": [1, 2, 3]
       		}
       	}
}

Which can then be fed to other tools (httpie for example).

Installation

Head to the releases page and grab the latest build for your platform. For the time being, you'll have to rename the downloaded file from jg-${platform} to just jg. Move it somewhere in your PATH and ensure that it is executable.

An alternative way if you have go installed is to run go install github.com/jawher/jg

Generators

The generator expressions syntax resembles the JSON syntax with a few caveats:

• It uses the = sign instead of : to separate a field and its value
• Strings are not quoted (unless they contain spaces)
• Since values are treated as strings by default, other types (numbers, booleans, null) need to be prefixed with a :
• No commas required to separate elements of an object or array

Think of it as the lightweight JSON syntax you dreamt of !

Field

SYNTAX: field = value

Adds a field named field to the current object.

The value can be one of:

• Literal: will be treated a string by default, unless prefixed with : (for numbers, booleans and null)
• Object generator: see below for details
• Array generator: see below for details

EXAMPLES:

• name = foo: adds a field to a JSON object named foo containing the string value "foo"
• age = :42 : prefixing a value with : instructs jg to handle it as a raw value, i.e. as a number, a boolean or as null and not treat it like a string

Dotted field

SYNTAX: parent.child = value

Same as field, but also creates the intermediary objects.

If you need the field name to contain a dot, enclose it in quotes, e.g. "field.with.dot"=value

EXAMPLES:

customer.address.zip = 123: adds a field named customer containing an object with an address field, itself an object with one zip field.

Object

SYNTAX field = { GENERATORS... }

Creates a JSON object. To set the object fields, specify the required generator expressions inside the brackets. The accepted generators are field generators.

EXAMPLES:

customer = { name=foo, age=:30 }

Array

SYNTAX field = [ GENERATORS... ]

Creates a JSON array.

To set the array elements, specify the required generator expressions inside the square brackets. The accepted generators are:

• literal: will be added as is to the array
• field generator: will add a JSON object containing the generated field as an element
• object generator: will add a the generated JSON object as an element
• array generator: will add a the generated JSON array as an element

EXAMPLES:

• tags = [ foo bar qix ]: creates an array containing the 3 strings "foo", "bar" and "qix".
• ids = [ :1 :2 :3 ]: prefix the literals with : to handle them as raw, i.e. number values
• results = [ id=:1 id=:2]: creates an array containing 2 objects, each with one field named id
• results = [ {id=:1 name=foo} {id=:2 name=bar}]: creates an array containing 2 objects, each with 2 fields id and name

CLI usage

Pretty-print

By default, jg outputs unindented JSON in a single line. The -p can be used to instruct jg to pretty-print the generated JSON.

One object mode

Calling jg with one or multiple field generators (field = value) results in producing a single JSON object

jg foo=a bar=c

produces a single JSON object with 2 fields:

{"bar":"c","foo":"a"}

Multiple objects/arrays

jg can also be made to generate one or multiple JSON objects or arrays by using the object and array delimiters ({} and []) at the top level:

Objects:

jg {foo=a} {bar=c}

{"foo":"a"}
{"bar":"c"}

Arrays (The generator expression is singled-quoted to avoid the shell trying to interpret it):

jg '[foo=a] [bar=c]'

[{"foo":"a"}]
[{"bar":"c"}]

License

This work is published under the MIT license.

Please see the LICENSE file for details.