Curl: how to pass value of specific key from file - bash

Question

wasn't able to find and I'm not sure if it possible at all. I know that I can pass the whole payload via #file.json, something like
$ curl -X POST -H "Content-Type: application/json" -d #test.json \
http://localhost/api/v3/endpoint
$ cat test.json
{
"key1": "value1",
"key2": "value2"
}
But now I need to upload gpg public key and I can't store the key inside test.json. What I need is something like
$ curl -X POST -H "Content-Type: application/json" \
http://localhost/api/v3/endpoint \
-d '{"key1": "value1", "key2": "#gpg-public.key"}'
Thanks in advance
As an option in bash I can use the following
$ curl -X POST -H "Content-Type: application/json" \
http://localhost/api/v3/endpoint \
-d "{\"key1\": \"value1\", \"key2\": \"$(cat gpg-public.key)\"}"
but I'm looking for more elegant way

Answer 1

I can't say this is more elegant, but at least it's different.
jq -Rn '{key2: input}' <pgp-public.key |
jq -s '.[0] * .[1]' test.json - |
curl -d #- ...
Credit for the jq hacks: Simo Kinnunen's answer here and Charles Duffy's answer here.

Answer 2

The first rule of JSON is to use a tool that knows JSON to generate dynamic values. A good tool is jq. Now, instead of storing a JSON file on disk, store a jq filter that can act as a template for your JSON file.
# test.jq
{
key1: "value1",
key2: $gpg
}
Now, you can run jq using this template as a filter, and supply a value for it to replace $gpg:
$ jq -n -f test.jq --arg gpg hi
{
"key1": "value1",
"key2": "hi"
}
Once you have this command, you can use it to pass the generated JSON directly to curl via standard input; the -d option can take #- as an argument to read from standard input.
jq -n -f test.q --arg gpg hi | curl ... -d #-
For simple jobs, you can specify the filter on the command line instead of reading it from a file.
jq -n '{key1: "value1", key2: $gpg}' --arg gpg hi | curl -d #-

Answer 3

use multipart/form-data with the -F parameter, it supports uploading multiple files at once.
curl -F json=#test.json -F pgp=#pgp-public.key http://localhost/api/v3/endpoint
ofc, the API endpoint will also need to support multipart/form-data for this to work.
edit: going by your comments, if you have to send a single json file, then edit the json file as needed and send the edited version, unfortunately bash is not a suitable language for editing json (although i'm sure it's possible), i'd recommend using some other scripting language for that. here's an example with php-cli to edit the json, then sending the edited json to curl via stdin:
php -r '$p=json_decode(file_get_contents("test.json"),true);$p["key2"]=file_get_contents("pgp-public.key");echo json_encode($p);' |
curl -d #- -X POST -H "Content-Type: application/json" http://localhost/api/v3/endpoint
(but any language with json support should suffice, like python/perl/php)