json2bash.sh

# Two functions for reading multiple variables out of a json stream with a single `jq` execution
# One reads them to an associated array and one to named vars


# Extract certain fields from json (STDIN) to a bash associated array
# Args:
# - out (nameref assoc-array) where results are written to.
# - rest is pairs of jq expressions to aa keys (to index into "out").
#   The jq expressions must result in leaf-values that can be printed.
function json2aa {
    if [[ "$(declare -p "${1}")" != "declare -A"* ]]; then
        echo "json2aa: passed nameref (${1}) is not of an associated array" >&2
        return 1
    fi
    local -n out="${1}"; shift
    local -a keys=()
    local jq_expr='['
    if [ $(( ${#} % 2 )) -ne 0 ]; then
        echo "json2aa: not en even number of remaining args" >&2
        return 1
    fi

    while [ ${#} -ge 2 ]; do
        jq_expr+="${1}"; shift
        keys+=( "${1}" ); shift
        [ ${#} -gt 1 ] && jq_expr+=','
    done
    jq_expr+='] | join("\n")'

    # now jq_expr should be an array of expressions that is then 'join'ed with newlines
    local -i idx=0
    local value
    while read -r value; do
        out["${keys[idx]}"]="${value}"
        (( idx++ ))
    done < <(jq -r "${jq_expr}")

    return 0
}

# Extract certain fields from json (STDIN) to a bash associated array
# Args are pairs of jq expressions and variable namerefs.
# The jq expressions must result in leaf-values that can be printed.
# The variables are expected to exist in caller's scope
function read_json {
    local -a names=()
    local jq_expr='['
    if [ $(( ${#} % 2 )) -ne 0 ]; then
        echo "json2aa: not en even number of remaining args" >&2
        return 1
    fi

    while [ ${#} -ge 2 ]; do
        names+=( "${1}" ); shift
        jq_expr+="${1}"; shift
        [ ${#} -gt 1 ] && jq_expr+=','
    done
    jq_expr+='] | join("\n")'

    # now jq_expr should be an array of expressions that is then 'join'ed with newlines
    local -i idx=0
    local value
    while read -r value; do
        local -n var="${names[idx]}"
        var="${value}"
        (( idx++ ))
    done < <(jq -r "${jq_expr}")

    return 0
}