Reading JSON data in a shell script

Question

I have a JSON file containing data about some images:

{
    "imageHeight": 1536,
    "sessionID": "4340cc80cb532ecf106a7077fc2a166cb84e2c21",
    "bottomHeight": 1536,
    "imageID": 1,
    "crops": 0,
    "viewPortHeight": 1296,
    "imageWidth": 2048,
    "topHeight": 194,
    "totalHeight": 4234
}

I wish to process these values in a simple manner in a shell script. I searched online but was not able to find any simple material to understand.

EDIT : What I wish to do with the values ?

I'm using convert (Imagemagick) to process the images. So, the whole workflow is something like. Read the an entry say crop from a line in the json file and then use the value in cropping the image :

convert -crop [image width from json]x[image height from json]+0+[crop value from json] [session_id from json]-[imageID from json].png [sessionID]-[ImageID]-cropped.png

I highly rate jq for working with JSON in a shell: stedolan.github.io/jq — cmbuckley
– cmbuckley, Commented Jun 25, 2014 at 10:56
Is using python or perl an option? They both have very good support for working with json-files. json-support is not supported natively in either awk, grep or shell. — Fredrik Pihl
– Fredrik Pihl, Commented Jun 25, 2014 at 10:56
You may provide solutions in python also , it might be helpful :) — anirudh_raja
– anirudh_raja, Commented Jun 25, 2014 at 10:57
...also, what would you like to do with the values, i.e. what is your expected outcome? Please update your question. Right now we are just guessing. — Fredrik Pihl
– Fredrik Pihl, Commented Jun 25, 2014 at 10:57
@cbuckley Please can you provide an example on how to process a field in a line in the json file — anirudh_raja
– anirudh_raja, Commented Jun 25, 2014 at 10:58

hek2mgl · Accepted Answer · 2014-06-25 11:02:50Z

2

I would recommend using jq. For example, to get the imageHeight, you can use:

jq ".imageHeight" data.json

Output:

If you want to store the value in a shell variable use:

variable_name=$(jq ".imageHeight" data.json)

answered Jun 25, 2014 at 11:02

hek2mgl

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Fredrik Pihl · Accepted Answer · 2014-06-25 12:32:21Z

1

Python-solution

import json
from pprint import pprint
json_data=open('json_file')
data = json.load(json_data)
pprint(data)
data['bottomHeight']

output:

In [28]: pprint(data)
{u'bottomHeight': 1536,
 u'crops': 0,
 u'imageHeight': 1536,
 u'imageID': 1,
 u'imageWidth': 2048,
 u'sessionID': u'4340cc80cb532ecf106a7077fc2a166cb84e2c21',
 u'topHeight': 194,
 u'totalHeight': 4234,
 u'viewPortHeight': 1296}

In [29]: data['bottomHeight']
Out[29]: 1536

answered Jun 25, 2014 at 12:32

Fredrik Pihl

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