Simple handy jq functions.

jq_functions.sh

declare -r SOME_JSON_FILE="/path/to/json/file.json"

# Read a key from a file.
# Usage: _key_value=$(_read_json_key "key")
function _read_json_key() {
  local -r _key="${1}"
  jq --arg key "${_key}" -r '.[$key]' "${SOME_JSON_FILE}"
}

# Writes a json key into an existing file without overwriting.
# Usage: _write_json_key "key" "value"
function _write_json_key() {
  local -r _key="${1}"
  local -r _val="${2}"
  local -r _temp="/tmp/.tmpfile.json"

  echo "Writing ${_key}:${_val} to json file..."
  jq \
    --arg key "${_key}" \
    --arg val "${_val}" \
    '.[$key] = $val' "${SOME_JSON_FILE}" > "${_temp}"
  mv -v "${_temp}" "${SOME_JSON_FILE}"

  return 0
}