JSON diff and patch Joseph Burnett

Note: to include the UI when building from source, use the Makefile.

Command line usage

Usage: jd [OPTION]... FILE1 [FILE2]
Diff and patch JSON files.

Prints the diff of FILE1 and FILE2 to STDOUT.
When FILE2 is omitted the second input is read from STDIN.
When patching (-p) FILE1 is a diff.

Options:
  -color       Print color diff.
  -p           Apply patch FILE1 to FILE2 or STDIN.
  -o=FILE3     Write to FILE3 instead of STDOUT.
  -set         Treat arrays as sets.
  -mset        Treat arrays as multisets (bags).
  -setkeys     Keys to identify set objects
  -yaml        Read and write YAML instead of JSON.
  -port=N      Serve web UI on port N
  -precision=N Maximum absolute difference for numbers to be equal.
               Example: -precision=0.00001
  -f=FORMAT    Read and write diff in FORMAT "jd" (default), "patch" (RFC 6902) or
               "merge" (RFC 7386)
  -t=FORMATS   Translate FILE1 between FORMATS. Supported formats are "jd",
               "patch" (RFC 6902), "merge" (RFC 7386), "json" and "yaml".
               FORMATS are provided as a pair separated by "2". E.g.
               "yaml2json" or "jd2patch".

Examples:
  jd a.json b.json
  cat b.json | jd a.json
  jd -o patch a.json b.json; jd patch a.json
  jd -set a.json b.json
  jd -f patch a.json b.json
  jd -f merge a.json b.json

Command Line Option Details

setkeys This option determines what keys are used to decide if two objects 'match'. Then the matched objects are compared, which will return a diff if there are differences in the objects themselves, their keys and/or values. You shouldn't expect this option to mask or ignore non-specified keys, it is not intended as a way to 'ignore' some differences between objects.

Library usage

Note: import only release commits (v2.Y.Z) because master can be unstable.

Note: the v2 library replaces the v1 (lib) library. V2 adds diff context, minimal array diffs and hunk-level metadata. However the format is not backward compatable. You should use v2.

import (
	"fmt"
	jd "github.com/josephburnett/jd/v2"
)

func ExampleJsonNode_Diff() {
	a, _ := jd.ReadJsonString(`{"foo":["bar"]}`)
	b, _ := jd.ReadJsonString(`{"foo":["baz"]}`)
	fmt.Print(a.Diff(b).Render())
	// Output:
	// @ ["foo",0]
	// [
	// - "bar"
	// + "baz"
	// ]
}

func ExampleJsonNode_Patch() {
	a, _ := jd.ReadJsonString(`["foo"]`)
	diff, _ := jd.ReadDiffString(`
@ [1]
  "foo"
+ "bar"
]
`)
	b, _ := a.Patch(diff)
	fmt.Print(b.Json())
	// Output:
	// ["foo","bar"]
}

Diff language

Note: this is the v1 grammar. Needs to be updated with v2.

• A diff is zero or more sections
• Sections start with a @ header and the path to a node
• A path is a JSON list of zero or more elements accessing collections
• A JSON number element (e.g. 0) accesses an array
• A JSON string element (e.g. "foo") accesses an object
• An empty JSON object element ({}) accesses an array as a set or multiset
• After the path is one or more removals or additions, removals first
• Removals start with - and then the JSON value to be removed
• Additions start with + and then the JSON value to added

EBNF

Diff ::= ( '@' '[' ( 'JSON String' | 'JSON Number' | 'Empty JSON Object' )* ']' '\n' ( ( '-' 'JSON Value' '\n' )+ | '+' 'JSON Value' '\n' ) ( '+' 'JSON Value' '\n' )* )*

Examples

@ ["a"]
- 1
+ 2

@ [2]
[
+ {"foo":"bar"}
]

@ ["Movies",67,"Title"]
- "Dr. Strangelove"
+ "Dr. Evil Love"
@ ["Movies",67,"Actors","Dr. Strangelove"]
- "Peter Sellers"
+ "Mike Myers"
@ ["Movies",102]
  {"Title":"Terminator","Actors":{"Terminator":"Arnold"}}
+ {"Title":"Austin Powers","Actors":{"Austin Powers":"Mike Myers"}}
]

@ ["Movies",67,"Tags",{}]
- "Romance"
+ "Action"
+ "Comedy"

Cookbook

Use git diff to produce a structural diff:

git difftool -yx jd @ -- foo.json
@ ["foo"]
- "bar"
+ "baz"

See what changes in a Kubernetes Deployment:

kubectl get deployment example -oyaml > a.yaml
kubectl edit deployment example
# change cpu resource from 100m to 200m
kubectl get deployment example -oyaml | jd -yaml a.yaml

output:

@ ["metadata","annotations","deployment.kubernetes.io/revision"]
- "2"
+ "3"
@ ["metadata","generation"]
- 2
+ 3
@ ["metadata","resourceVersion"]
- "4661"
+ "5179"
@ ["spec","template","spec","containers",0,"resources","requests","cpu"]
- "100m"
+ "200m"
@ ["status","conditions",1,"lastUpdateTime"]
- "2021-12-23T09:40:39Z"
+ "2021-12-23T09:41:49Z"
@ ["status","conditions",1,"message"]
- "ReplicaSet \"nginx-deployment-787d795676\" has successfully progressed."
+ "ReplicaSet \"nginx-deployment-795c7f5bb\" has successfully progressed."
@ ["status","observedGeneration"]
- 2
+ 3

apply these change to another deployment:

# edit file "patch" to contain only the hunk updating cpu request
kubectl patch deployment example2 --type json --patch "$(jd -t jd2patch ~/patch)"