Getting Started

Getting Started

jp is a commmand-line tool

It requires node.js to be to be installed. The minimum tested version is 6.0, so any version above this should work.

To install it:

npm install -g json-processing

Then test it with:

$ echo '{ "hello": "world" }' | jp -l 'select()' -m json
{"hello":"world"}

Processing Script

Every jp processing script is a javascript that starts with a call to the select() function. In general, the function takes a yajs selection path (no need for the leading $) that select objects from a JSON streaming and feed them to an instance of Rx.Observable, that is returned by the function to be further augmented with processing instructions.

The select() function is defined as:

select(path: string = '$', input: Stream = process.stdin): Rx.Observable

• Arguments

name	description	default
path	A yajs selection path	$
input	A Node.js Stream	process stdin

• Returns

Returns a Rx.Observable

• Examples

1. Pick an array of strings and upper case all the elements

   Input: {"strings": [ "a", "b", "c" ]}

   Script: select(".strings").map(s => s.toUpperCase())

   Output: "A" "B" "C"

2. Pick an array of numbers and sum all the elements

   Input: {"numbers": [ 1, 2, 3 ]}

   Script: select(".numbers").reduce((a, b) => a + b, 0)

   Output: 6

Basic Command-Line Usage

The basic command-line usage of the jp tool is simply piping data to the tool with a defined processing script (either inline or [in a script file]):

Inline Script

A script can be defined inline using the -l parameter:

$ echo '{"strings": [ "a", "b", "c" ]}' | jp -l 'select(".strings").map(s => s.toUpperCase())' -m json
"A"
"B"
"C"

File Script

A script can also be defined in a js file. The file must end with .js and it must export the processing function:

module.exports = () => select(".strings").map(s => s.toUpperCase())

$ echo '{"strings": [ "a", "b", "c" ]}' | jp ./process.js -m json
"A"
"B"
"C"