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Generate and apply diffs between JSON documents.
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Aeson Diff

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This is a small library for working with changes to JSON documents. It includes a library and two executables in the style of diff(1) and patch(1). Patches are themselves JSON Patch documents as specified in RFC 6902.


The aeson-diff package is written in Haskell and can be installed using the Cabal package management tool, stack, or something similar.

stack install aeson-diff

The command-line tools can then be executed using stack:

stack exec json-diff -- ....
stack exec json-patch -- ....

If you prefer to use Cabal, something like this might do the trick:

cd aeson-diff/
cabal sandbox init
cabal install --dependencies-only
cabal build
sudo mkdir -p /usr/local/bin
sudo cp dist/build/json-*/json-{diff,patch} /usr/local/bin/


Patch format

aeson-diff supports the JSON Patch format described in RFC 6902.

json-diff command

The json-diff command compares two JSON documents and extracts a patch describing the differences between the first document and the second.

Usage: json-diff [-T|--test-before-remove] [-o|--output OUTPUT] FROM TO
Generate a patch between two JSON documents.

Available options:
    -h,--help                Show this help text
    -T,--test-before-remove  Include a test before each remove.
    -o,--output OUTPUT       Write patch to file OUTPUT.

json-patch command

The json-patch command applies a patch describing changes to be made to a JSON document.

Usage: json-patch [-o|--output OUTPUT] PATCH FROM
Generate a patch between two JSON documents.

Available options:
  -h,--help                Show this help text
  -o,--output OUTPUT       Destination for patched JSON.
  PATCH                    Patch to apply.
  FROM                     JSON file to patch.

aeson-diff library

The aeson-diff library exports as single module: Data.Aeson.Diff. This exports diff and patch functions which do exactly what might be expected:

  • diff :: Value -> Value -> Patch examines source and target JSON Values and constructs a new Patch describing the changes.

  • patch :: Patch -> Value -> Result Value applies the changes in a Patch to a JSON Value. If an error results then an exception is thrown.

For more complete information, see the documentation.

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