mktemp with extension without specifying file path

Prefacing this with that I found identical questions but none of them have answers that are working for me.

I need to make a temporary .json file (it needs to be json because I'll be working with jq later in the script).

I thought based on the answers to this question that it would be the following, but they're creating files named .json and XXXXXXXX.json respectively.

STACKS=$(mktemp .json)
STACKS=$(mktemp XXXXXXXX.json)

This will need to run on both mac OS, and a linux box. I can't specify a path for the file because it will be run both locally and by Jenkins, which have an unidentical file structure. What's the proper syntax?

Solution

if you are using openBSD mktemp you can

STACKS="$(mktemp XXXXXX).json"

and then write a trap so the tmps are removed when script finishes:

function cleanup {
    if [ -f "$STACKS" ] && [[ "$STACKS" =~ ".json"$ ]]; then
        rm -f "$STACKS"
    fi
}
trap cleanup EXIT

so when script finishes (no matter how) it will try to remove $STACKS if it is a file and if it ends with .json (for extra safety).