Merge parts from one or more JSON files together. I use `grunt-update-json` to keep my `Bower.json` and `component.json` in sync with `package.json`.

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Merge parts from one or more JSON files together. I use grunt-update-json to keep my bower.json and component.json in sync with package.json.
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Upgrading from 1.x

The semantics of Object Groupings have been reversed:
  • was {from: "to"}
  • now`{to: "from"}

Getting Started

npm install grunt-update-json --save-dev

I highly favor using the fabulous load-grunt-tasks over the tiring and cumbersome grunt.loadNpmTasks. Your grunt tasks are all in your package.json, so let's embrace DRY:
npm install load-grunt-tasks --save-dev

// Gruntfile.js
module.exports = function (grunt) {
    require('load-grunt-tasks')(grunt); // load all grunt tasks. Done!

Using the update_json task

In your awesome project's Gruntfile, add a section named update_json:
// Gruntfile.js
  update_json: {
    // set some task-level options
    options: {
      src: 'package.json',
      indent: '\t'
    // update bower.json with data from package.json
    bower: {
      src: 'package.json',    // where to read from
      dest: 'bower.json',     // where to write to
      // the fields to update, as a String Grouping
      fields: 'name version description repository'
    // update component.json with data from package.json
    // component.json fields are a named a bit differently from
    // package.json, so let's tell update_json how to map names
    component: {
      // reuse the task-level `src`
      dest: 'component.json',      // where to write to
      fields: {                    // the fields to update
        // notice how this time we're passing a hash instead
        // of an array; this allows us to map the field names.
        // We still specify all the names we want, and additionally
        // we also specify the target name in the detination file.
        // to            from
        // -----------   -------------------
        'name'            : null,         // null means 'leave as is'
        'description'     : 'description',// but feel free to type the field name twice
        'repository'      : 'repo',       // rename 'repository' to 'repo'
        'version'         : null,
        'keywords'        : null,
        'main'            : null,
        'dependencies'    : null,
        'development'     : 'devDependencies',
        'license'         : null,
    // `composer` has the same data as `package`, but has some tricky
    // semantics
    composer: {
      // again, reuse the task-level `src`
      dest: 'composer.json',
      // the fields in an Array Grouping with some embedded Object Groupings
      fields: [
          name: function(src){
            return src.repository.url.match(/([^\/]+\/[^\/]+).git/)[1];
          license: 'licenses/0/type',
          authors: [{
            name: 'author/name',
            homepage: 'author/url'



Like most Grunt tasks, options can be specified at the update_json level and/or at the update_json:<target> level. Target-level options override task-level options.


By default, output will not be pretty-printed. Specify a value here to have indentation applied:
update_json: {options: {indent: "\t"}}
or for spaces:
update_json: {options: {indent: "  "}}

Source Data

An input JSON file. May be a list, which will be _.mergedmerge together.

Destination Data

An output JSON file.

Field Groupings

an ordered collection of field specifications, which can optionally contain additional lists of fields.

Object Grouping

{fields: {field: null, another: "yetanother"}}
A list of field specs, pointing at any other kind of field specification.

Array Grouping

{fields: ["field", "another", "still another > yet another"]}
Create field copies, or field renames, of each of the listed fields.

String Grouping

{fields: "field, another, still another > yetanother"}
Create field copies, or field renames, of each of the listed fields.

The most concise way to copy/rename a number of fields of simple JSON documents
  • Can't handle fields with , or > in their names.
  • Can't handle most complex field paths.

Field Specifications

The canonical Object Grouping format is used here: some specifications are not compatible with some Groupings.

Field Copy

{field: null}
Create or replace field in dest from the value of field in src.

Field Rename

{renamed: "original"} or "original > renamed" String Grouping only
Create or replace renamed in dest with the value of original from src.

Field Pointer

{field: "/some/deep/field"}
Create or replace field in dest from some/deep/field in src.

A field spec destination which starts with / will be interepreted as a json-pointer.
To select a field that begins with a literal /, escape with a single \ (written \\):
{field: "\\/a"}

Field Path

{field: "$.some.path[(@.with='filters')]"}
Create or replace field in dest with the value of nodes found with a JSONPath query

A field spec destination which starts with $. will be interpreted as a JSONPath selector.
To select a field that begins with a literal $., escape with a single \ (written \\):
{field: "\\$.a"}

Field Collapse

{field: ["first", "second"]}
Create or replace an array named field in dest with the values of first and second from src.

Field Construct

{field: {first: "first", second: "second"}}
Create or merge an object field in dest with labeled first and second with their respective values from src

Field Function

{field: function(src){ return src.field; }}
Create a field named field that is the output of running a function against src.

If all else fails, you can supply a function which will called with a copy of the combined source object.
update_json: {
  composer: {
    src: "package.json",
    dest: "composer.json",
    fields: {
      name: function(src){
        // pull username/repo off a github url
        return src.repository.url.match(/([^\/]+\/[^\/]+).git/)[1];

Ideas for improvement


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