jq add or update a value with multiple --arg

Question

I have file.json in the structure of:

{
  "connections": {}
}

I want to update the connections object with variables $1 and $2. I'm trying:

jq --arg ssid "$1" --arg pass "$2" '.connections.$ssid = "$pass"' file.json > tmp.json && mv tmp.json file.json

But I'm getting back jq: error: syntax error, unexpected '$', expecting FORMAT or QQSTRING_START (Unix shell quoting issues?) at <top-level>, line 1: .connections.$ssid = "$pass"

I'm expecting script.sh value key to produce:

{
  "connections": {key:"value"}
}

How can I update the object with multiple arguments

Answer 1

You have to use [] indexing to use variables (or anything non-literal) as the key:

jq --arg ssid abc --arg pass 123 '.connections[$ssid] = $pass' < file.json
{
  "connections": {
    "abc": "123"
  }
}

Here [$ssid] indexes into .connections with the value of $ssid as the key. The error was at ".$", which is a syntax error, rather than to do with multiple variables.

Variables aren't substituted in directly as strings in the way they might be in a shell script, but are actual named lexical bindings that have to be used in expression context. The index could be a more complex expression: .connections[$ssid + "X"] = $pass would put an X on the end first and use that as the key.