Jq update JSON key:value based on value - json

Question

I'm pretty new to jq and wanted to use it to update an AWS ECS task definition with a new value. AWS cli returns the following json response and i would like to modify the object with name property CONFIG_URL with value "this is atest".
{
"family": "contentpublishing-task",
"volumes": [],
"containerDefinitions": [
{
"environment": [
{
"name": "TEST_ENV",
"value": "TEST"
},
{
"name": "CONFIG_URL",
"value": "s3://stg-appcfg/config-20160729-1130.json"
}
],
"name": "contentpublishing",
"mountPoints": [],
"image": "contentpublishing:blah",
"cpu": 512,
"portMappings": [
{
"protocol": "tcp",
"containerPort": 8081,
"hostPort": 8080
}
],
"memory": 256,
"essential": true,
"volumesFrom": []
}
]
}
Tried the following query
cat test.json | jq 'select(.containerDefinitions[0].environment[].name=="CONFIG_URL").value|="this is atest"' 2>&1
But following has been returned. As you can see an additional value key is added the outer most json object.
{
"family": "contentpublishing-task",
"volumes": [],
"containerDefinitions": [
{
"environment": [
{
"name": "TEST_ENV",
"value": "TEST"
},
{
"name": "CONFIG_URL",
"value": "s3://stg-appcfg/config-20160729-1130.json"
}
],
"name": "contentpublishing",
"mountPoints": [],
"image": "contentpublishing:blah",
"cpu": 512,
"portMappings": [
{
"protocol": "tcp",
"containerPort": 8081,
"hostPort": 8080
}
],
"memory": 256,
"essential": true,
"volumesFrom": []
}
],
"value": "this is atest"
}

Answer 1

You have to select the corresponding environment node first before setting the value. Your query doesn't change the context so it's still on the root item so you end up adding the new value to the root.
$ jq --arg update_name "CONFIG_URL" --arg update_value "this is a test" \
'(.containerDefinitions[].environment[] | select(.name == $update_name)).value = $update_value' input.json

Answer 2

Here is a solution which uses jq Complex assignments
(
.containerDefinitions[]
| .environment[]
| select(.name == "CONFIG_URL")
| .value
) |= "this is atest"