How to replace parameter of a json file by a shell script?

Question

Let's say 123.json with below content:

{
  "LINE" : {
    "A_serial" : "1234",
    "B_serial" : "2345",
    "C_serial" : "3456",
    "X_serial" : "76"
  }
}

If I want to use a shell script to change the parameter of X_serial by the original number +1 which is 77 in this example. I have tried the below script to take out the parameter of X_serial:

grep "X_serial" 123.json | awk {print"$3"}

which outputs 76. But then I don't know how to make it into 77 and then put it back to the parameter of X_serial.

Cross posted: unix.stackexchange.com/q/590365

user13663050
– user13663050

2020-06-02 05:25:53 +00:00
Commented Jun 2, 2020 at 5:25 — user13663050
– user13663050, Commented Jun 2, 2020 at 5:25
Why are the numbers strings and not integers?

RoadRunner
– RoadRunner

2020-06-02 06:42:42 +00:00
Commented Jun 2, 2020 at 6:42 — RoadRunner
– RoadRunner, Commented Jun 2, 2020 at 6:42

oguz ismail · Accepted Answer · 2020-06-02 04:32:11Z

9

It's not a good idea to use line-oriented tools for parsing/manipulating JSON data. Use jq instead, for example:

$ jq '.LINE.X_serial |= "\(tonumber + 1)"' 123.json
{
  "LINE": {
    "A_serial": "1234",
    "B_serial": "2345",
    "C_serial": "3456",
    "X_serial": "77"
  }
}

This simply updates .LINE.X_serial by converting its value to a number, increasing the result by one, and converting it back to a string.

edited Jun 2, 2020 at 4:32

answered Jun 2, 2020 at 4:17

oguz ismail

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4 Comments

Owen Over a year ago

If I don't have the tool jq processor, what other command can i use?

oguz ismail Over a year ago

@Owen No idea, python maybe.

Gilles Quénot Over a year ago

jq can be downloaded as standalone tool

thoroc Over a year ago

For anyone else reading this: If the json data is coming from another source, you can pipe it to jq and eventually output it to a different file. Just don't forget the leading . char.

user229044 · Accepted Answer · 2020-06-02 13:04:41Z

3

You need to install powerful JSON querying processor like jq processor. you can can easily install from here

once you install jq processor, try following command to extract the variable from JSON key value

value=($(jq -r '.X_serial' yourJsonFile.json))

you can modify the $value as you preferred operations

edited Jun 2, 2020 at 13:04

user229044♦

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answered Jun 2, 2020 at 4:16

Melan Rashitha

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Comments

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

With pure Javascript: nodejs and bash :

node <<EOF
var o=$(</tmp/file);
o["LINE"]["X_serial"] = parseInt(o["LINE"]["X_serial"]) + 1;
console.log(o);
EOF

Output

{ LINE:
   { A_serial: '1234',
     B_serial: '2345',
     C_serial: '3456',
     X_serial: 78 }
}

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Jun 2, 2020 at 16:05

Gilles Quénot

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Comments

P2000 · Accepted Answer · 2020-06-03 19:04:39Z

0

sed or perl, depending on whether you just need string substitution or something more sophisticated, like arithmetic.

Since you tried grep and awk, let's start with sed:

In all lines that contain TEXT, replace foo with bar

sed -n '/TEXT/ s/foo/bar/ p'

So in your case, something like:

sed -n '/X_serial/ s/\"76\"/\"77\"/ p'

or

$ cat 123.json | sed  '/X_serial/ s/\"76\"/\"77\"/' > new.json

This performs a literal substiution: "76" -> "77"

If you would like to perform arithmetic, like "+1" or "+10" then use perl not sed:

$ cat 123.json | perl -pe 's/\d+/$&+10/e if /X_serial/'
{
  "LINE" : {
    "A_serial" : "1234",
    "B_serial" : "2345",
    "C_serial" : "3456",
    "X_serial" : "86"
  }
}

This operates on all lines containing X_serial (whether under "LINE" or under something else), as it is not a json parser.

edited Jun 3, 2020 at 19:04

answered Jun 2, 2020 at 4:37

P2000

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2 Comments

Owen Over a year ago

Since the value of "X_serial" will change which means i can't use exactly "76\", Any other suggestion?

P2000 Over a year ago

@Owen, Ok, I edited it to include arithmetic. I personally prefer using shell tools (like awk, sed, perl etc...) over jq whenever the task can be done with them. But if you need to read the json to find only X_serial under LINE, then yes you have to use jq or some other json parsing tool.

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