Everyone I know prefers to work with JSON over XML, but sadly there is a sore lack of utilities of the quality or depth of html-xml-utils and XMLStarlet for actually processing JSON data in an automated fashion, short of writing an ad hoc processor in your favourite programming language.
jsonpipe is a step towards a solution: it traverses a JSON object and produces a simple, line-based textual format which can be processed by all your UNIX favourites like grep, sed, awk, cut and diff. It may also be valuable within programming languages---in fact, it was originally conceived as a way of writing simple test assertions against JSON output without coupling the tests too closely to the specific structure used.
This implementation (which should be considered the reference) is written in Python.
A <pre> is worth a thousand words. For simple JSON values:
$ echo '"Hello, World!"' | jsonpipe / "Hello, World!" $ echo 123 | jsonpipe / 123 $ echo 0.25 | jsonpipe / 0.25 $ echo null | jsonpipe / null $ echo true | jsonpipe / true $ echo false | jsonpipe / false
The 'root' of the object tree is represented by a single / character, and
for simple values it doesn't get any more complex than the above. Note that a
single tab character separates the path on the left from the literal value on
the right.
Composite data structures use a hierarchical syntax, where individual keys/indices are children of the path to the containing object:
$ echo '{"a": 1, "b": 2}' | jsonpipe
/ {}
/a 1
/b 2
$ echo '["foo", "bar", "baz"]' | jsonpipe
/ []
/0 "foo"
/1 "bar"
/2 "baz"
For an object or array, the right-hand column indicates the datatype, and will
be either {} (object) or [] (array). For objects, the order of the keys
is preserved in the output.
The path syntax allows arbitrarily complex data structures:
$ echo '[{"a": [{"b": {"c": ["foo"]}}]}]' | jsonpipe
/ []
/0 {}
/0/a []
/0/a/0 {}
/0/a/0/b {}
/0/a/0/b/c []
/0/a/0/b/c/0 "foo"
Because the path components are separated by / characters, an object key
like "abc/def" would result in ambiguous output. jsonpipe will throw
an error if this occurs in your input, so that you can recognize and handle the
issue. To mitigate the problem, you can choose a different path separator:
$ echo '{"abc/def": 123}' | jsonpipe -s '☃'
☃ {}
☃abc/def 123
The Unicode snowman is chosen here because it's unlikely to occur as part of
the key in most JSON objects, but any character or string (e.g. :, ::,
~) will do.
Another useful part of the library is jsonunpipe, which turns jsonpipe
output back into JSON proper:
$ echo '{"a": 1, "b": 2}' | jsonpipe | jsonunpipe
{"a": 1, "b": 2}
jsonunpipe also supports incomplete information (such as you might get from grep), and will assume all previously-undeclared parts of a path to be JSON objects:
$ echo "/a/b/c 123" | jsonunpipe
{"a": {"b": {"c": 123}}}
Since jsonpipe is written in Python, you can import it and use it without having to spawn another process:
>>> from jsonpipe import jsonpipe
>>> for line in jsonpipe({"a": 1, "b": 2}):
... print line
/ {}
/a 1
/b 2
Note that the jsonpipe() generator function takes a Python object, not a
JSON string, so the order of dictionary keys may be slightly unpredictable in
the output. You can use simplejson.OrderedDict to get a fixed ordering:
>>> from simplejson import OrderedDict
>>> obj = OrderedDict([('a', 1), ('b', 2), ('c', 3)])
>>> obj
OrderedDict([('a', 1), ('b', 2), ('c', 3)])
>>> for line in jsonpipe(obj):
... print line
/ {}
/a 1
/b 2
/c 3
A more general hint: if you need to parse JSON but maintain ordering for object
keys, use the object_pairs_hook option on simplejson.load(s):
>>> import simplejson
>>> simplejson.loads('{"a": 1, "b": 2, "c": 3}',
... object_pairs_hook=simplejson.OrderedDict)
OrderedDict([('a', 1), ('b', 2), ('c', 3)])
Of course, a Python implementation of jsonunpipe also exists:
>>> from jsonpipe import jsonunpipe
>>> jsonunpipe(['/\t{}', '/a\t123'])
{'a': 123}
You can pass a decoder parameter, as in the following example, where the
JSON object returned uses an ordered dictionary:
>>> jsonunpipe(['/\t{}', '/a\t123', '/b\t456'],
... decoder=simplejson.JSONDecoder(
... object_pairs_hook=simplejson.OrderedDict))
OrderedDict([('a', 123), ('b', 456)])
jsonpipe is written in Python, so is best installed using pip:
pip install jsonpipe
Note that it requires Python v2.5 or later (simplejson only supports 2.5+).
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