I use jq for reading and filtering json on the command line.
Given the json below, I’d like to update the value of b to be 30. jq offers the update assignment, |=, for this.
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{
"a": {
"b": 10
},
"c": 20
}
Try out the snippet at https://jqplay.org/s/t39OXPDrll-
Doing the same with that data saved to file, say myData.json and PowerShell and passing the new value as a jq variable would look like this:
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{
"a": {
"b": 10
},
"c": 20
}
In the command line, run the following:
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# retrieve b's value
C:\opt\jq-win64.exe '.a.b' myData.json
# set 30 to a powershell variable
$newValue = 30
# assign newValue to jq variable 'jqVarToUse' and pass it to the assigment operator
C:\opt\jq-win64.exe --arg jqVarToUse $newValue '.a.b |= $jqVarToUse' myData.json
jq gives the following output, and does not modify the original file.
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{
"a": {
"b": "30"
},
"c": 20
}
To let jq make the change and directly modify the file, enclose the update in cat. In bash, it looks like this:
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new_value=40
cat <<< "$(jq --arg jqVarToUse $newnew_valueValue '.a.b |= $jqVarToUse' myData.json)" > myData.json
What to watch out for: if there’s an error anywhere, the modified file (myData.json) will be empty.
Beware!
if there’s an error anywhere, the modified file (
myData.json) will be empty.