How to prevent escaping when adding JSON object with jq? - json

Question

I am working with jq and I am trying to add a new JSON object to a new key to an existing file.
I have the following JSON file, foobarbaz.json :
{
"example":{
"name": "stackOverflowQuestion"
}
}
I want to add a new entry under example, so to get the following output in foobar.json
{
"example": {
"name": "stackOverflowQuestion",
"new": {
"newfield": {
"key": "value"
}
}
}
}
I am using the following commands in the terminal:
$ tempvar='{"newfield":{"key":"value"}}'
$ cat foobarbaz.json | jq '.example.new=env.tempvar' > foobar.json
However, the output in foobar.json is somewhat unexpected:
{
"example": {
"name": "stackOverflowQuestion",
"new": "{\"newfield\":{\"key\":\"value\"}}"
}
}
Why does jq wrap the curly brackets with quotes, and why does it escape the double quotes?

Answer 1

Use fromjson to convert your string (the format all environment variables are in!) to the corresponding data structure, by decoding it as JSON content.
tempvar='{"newfield":{"key":"value"}}' jq '.example.new=(env.tempvar | fromjson)' <<'EOF'
{
"example":{
"name": "stackOverflowQuestion"
}
}
EOF
...emits as output:
{
"example": {
"name": "stackOverflowQuestion",
"new": {
"newfield": {
"key": "value"
}
}
}
}

Answer 2

Use the --argjson option to pass the pre-existing JSON snippet as a variable to the filter.
$ jq --argjson x "$tempvar" '.example.new=$x' foobarbaz.json
{
"example": {
"name": "stackOverflowQuestion",
"new": {
"newfield": {
"key": "value"
}
}
}
}
Note that tempvar isn't strictly necessary and can be dropped, if you are only defining it for use with the filter:
$ jq '.example.new={newfield: {key: "value"}}' foobarbaz.json
{
"example": {
"name": "stackOverflowQuestion",
"new": {
"newfield": {
"key": "value"
}
}
}
}