Extract a part of json and append a property in UNIX shell scripting

Question

I have a json, from which I need to extract a part and append/insert a new value into the existing array. My code is as follows,

{
    "itemId": "item_1",
    "itemName": "item 1",
    "itemPosition": [{
    "posId": "item_1_1",
    "rowPos": 0,
    "columnPos": 0
}, {
    "posId": "item_1_2",
    "rowPos": 0,
    "columnPos": 1
}, {
    "posId": "item_1_3",
    "rowPos": 1,
    "columnPos": 0
}, {
    "posId": "item_1_4",
    "rowPos": 1,
    "columnPos": 1
}]
}, {
"itemId": "item_2",
"itemName": "item 2",
"itemPosition": [{
    "posId": "item_2_1",
    "rowPos": 0,
    "columnPos": 0
}, {
    "posId": "item_2_2",
    "rowPos": 0,
    "columnPos": 1
}, {
    "posId": "item_2_3",
    "rowPos": 1,
    "columnPos": 0
}, {
    "posId": "item_2_4",
    "rowPos": 1,
    "columnPos": 1
}]
}

in this json i need to add a new value in itemPosition under the item id "item_1" like

{
    "posId": "item_1_5",
    "rowPos": 2,
    "columnPos": 1
}

I used following command to extract the json using string search like

cat sample.json | nl | sed -n '/"item_1"/,/"item_2"/p'

output is :

 2      "itemId": "item_1",
 3      "itemName": "item 1",
 4      "itemPosition": [{
 5          "posId": "item_1_1",
 6          "rowPos": 0,
 7          "columnPos": 0
 8      }, {
 9          "posId": "item_1_2",
10          "rowPos": 0,
11          "columnPos": 1
12      }, {
13          "posId": "item_1_3",
14          "rowPos": 1,
15          "columnPos": 0
16      }, {
17          "posId": "item_1_4",
18          "rowPos": 1,
19          "columnPos": 1
20      }]
21  }, {
22      "itemId": "item_2",

Question is how should I traverse into itemPosition array to find the last value in the array and append or insert a new value after that?

How would you feel about using a language which actually supports JSON, like Python, Ruby, Perl, etc.? — John Zwinck
– John Zwinck, Commented Jan 14, 2015 at 7:25
Thanks for your response John. Supposed to use shell scripting only. — Rajan
– Rajan, Commented Jan 14, 2015 at 8:27
Your json is broken: cat your.json | python -m json.tool returns Extra data: line 21 column 2 - line 41 column 2 (char 338 - 666) — user2243670
– user2243670, Commented Jan 14, 2015 at 10:24

vijaidhas · Accepted Answer · 2015-01-14 11:36:21Z

1

you can use the below code, if you dont have jq or any parser installed in your linux box. it should work for you requirement. kindly check.

line_to_be_replaced=`cat itemlist.json | nl |  sed -n '/"item_1"/,/"item_2"/p' | grep -in "}]" | awk '{print $2}'`
sed  -i "${line_to_be_replaced} s|.*|}, {\n\"posId\": \"item_1_5\",\n\"rowPos\": 2,\n\"columnPos\": 1\n}]|g" itemlist.json

Note: itemlist.json file contains the JSON code.

answered Jan 14, 2015 at 11:36

vijaidhas

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user2243670 · Accepted Answer · 2015-01-14 10:38:09Z

0

You can use jq to parse json in the shell. jq makes it possible to selectively append strings to a json file.

This code will achieve what you're trying to do:

cat your.json | jq '.itemPosition |= . + [{"posId":"item_1_5","rowPos": 2,"columnPos": 1}]'

edit: this works only for lines 1 to 21 of your json file which is broken from line 22 on.

edited Jan 14, 2015 at 10:38

answered Jan 14, 2015 at 10:10

user2243670

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