bash - Passing JSON arguments (not simple strings) to jq

Question

How do I pass in bash variables into a jq --arg parameter?

All I can get to work is this:

FINAL_JSON= #some JSON

PAYLOAD=$(echo $FINAL_JSON | jq ' {
"attachments": .
} ')

What's bothering me is that echo $FINAL_JSON thing. I should be able to pass in variables in jq??

PAYLOAD=$(jq -n --arg attach "$FINAL_JSON" '{ 
"attachments":$attach
}')

But all that does is pass the JSON in as a string. Without quotes " around the $FINAL_JSON I get this error:

error: syntax error, unexpected $end
{1 compile error

Answer 1

A simple transformation of your working code (also moving to lower-case variable names, as per convention for variable names not reserved for shell or system use):

payload=$(jq -n --argfile attach <(printf '%s
' "$final_json") '{ 
"attachments":$attach
}')

I'm sticking with --argfile here since it parses the file's contents as JSON; using --arg wouldn't have that effect.

The <(...) syntax is process substitution, which is replaced with a filename for a named pipe or temporary file connected to the content in question.

---

However, you can also use --arg, and apply the fromjson filter to parse as JSON:

payload=$(jq -n --arg attach "$final_json" '{ 
"attachments":$attach|fromjson
}')