Bash scripting grep variable from multilined json?

Question

I have a JSON file that has many instances like this..:

{
  "SensorApp": "Open Hardware Monitor",
  "SensorClass": "Temperature",
  "SensorName": "Intel Core i7-4790: CPU Core #4",
  "SensorValue": "31",
  "SensorUnit": "C",
  "SensorUpdateTime": 0
},
{
  "SensorApp": "Open Hardware Monitor",
  "SensorClass": "Temperature",
  "SensorName": "Intel Core i7-4790: CPU Package",
  "SensorValue": "32",
  "SensorUnit": "C",
  "SensorUpdateTime": 0
},
{
  "SensorApp": "Open Hardware Monitor",
  "SensorClass": "Clock",
  "SensorName": "Intel Core i7-4790: CPU Core #1",
  "SensorValue": "3899.165",
  "SensorUnit": "MHz",
  "SensorUpdateTime": 0
},

And so forth. I need to assign a variable, say var1 to the sensor value in:

{
  "SensorApp": "Open Hardware Monitor",
  "SensorClass": "Temperature",
  "SensorName": "Intel Core i7-4790: CPU Package",
  "SensorValue": "32",
  "SensorUnit": "C",
  "SensorUpdateTime": 0
},

I've tried a few questions already in stackoverflow, however none of them seem to work with multi-lined JSON files.

Any ideas how i can achieve this?

hek2mgl · Accepted Answer · 2015-06-23 08:44:16Z

6

I'm not sure if you want to change the value in the json file to a value of a shell variable or if you want to set a shell variable to the value of the SensorValue field in the json.

However, for both tasks you can use jq:

Iterating over json values in bash

jq -r '.[].SensorValue' file.json | while read -r value ; do
    # Do something useful with the value
    echo "$value"
done

Modifying a json file from bash

VALUE=123
jq ".[].SensorValue = $VALUE" file.json

Update: In comments you told you want to extract the SensorValue out of that json object where SensorName equals "Intel Core i7-4790: CPU Package". In jq you are using the select() function for that:

jq -r '.[] | select(.SensorName == "Intel Core i7-4790: CPU Package").SensorValue' file.json

Output:

edited Jun 23, 2015 at 8:44

answered Jun 20, 2015 at 13:38

hek2mgl

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2 Comments

cheesus Over a year ago

Thanks! Sorry, i wrote this question very late at night. I need to pull the values out of the json file. With your jq solution, how would i set it to only pull the value from a specific section? Right now it just spits back all the matching variables. For example, i only want the value immediately following " "Intel Core i7-4790: CPU Package",".

hek2mgl Over a year ago

@user2809413 What you have in mind is possible with jq and is one of it's key features. I have updated my answer and added an example. Note that jq is getting more and more a standard tool for working with json in the shell.

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