bash function which generates a json based on arguments

tojson.sh

#!/usr/bin/env bash

# Usage: make_event my-event test "hello world" -> {"name":"my-event","test":"hello world","unixtime":123}

make_event() {
    if ! (( "$#" % 2)); then
        echo "log_event expects an uneven number of arguments"
        echo "Usage: $0 <event-name> [[<key> <val>]...]"
        exit 1
    fi

    build_pairs() {
        if [[ "$#" -eq 1 ]]; then
            return
        fi

        echo --arg "var$1" "$2" --arg "val$1" \""$3"\" "$(build_pairs $(($1 + 1)) "${@:4}")"
    }

    build_pipeline() {
        if [[ "$#" -eq 1 ]]; then
            return
        fi

        echo ' | .[$'var$1'] = $'val$1 $(build_pipeline $(($1 + 1)) "${@:4}")

    }

    local PIPELINE=$(build_pipeline 0 "${@:2}")
    local PAIRS=$(build_pairs 0 "${@:2}")

    eval jq -c -n $PAIRS \
        --arg name "$1" \
        --arg unixtime "$(date +%s)" \
        --arg formattedtime \"$(date)\" \' \
        ' . | .["name"] = $name ' \
        ' | .["unixtime"] = $unixtime ' \
        ' | .["formattedtime"] = $formattedtime ' \
        "$PIPELINE"\' <<< "{}"
}

log_event() {
    EVENT="$(make_event "$@")"
    echo "$(date) BACKUP_EVENT|$EVENT"
    if [[ ! -z "$EVENT_LOG" ]]; then
        echo "$EVENT" >> "$EVENT_LOG"
    fi
}