client.on('message', pMessage => {
    if (executable(pMessage.content) == true) {
        execute(pMessage.content, pMessage.channel).then(sResult => { pMessage.channel.send(sResult) });
    }
});

async function execute(sMessage, pChannel = null) {

    // strip off the initial ! that marks the message as a command; whatever comes immediately afterwards is the command
    let args = sMessage.substring(1).trim().split(/ +/g);
    let cmd = args[0];
    // don't include the command itself among the rest of the arguments passed to it
    args = args.splice(1);

    // resolve nested commands first if they exist
    let sInnerCom = ""; // nested command input
    let sInnerComResult = ""; // nested command output
    if ((args.includes("[") == true) && (args.includes("]") == true)) { // consider anything in [ ] a nested command
        let iStart = args.indexOf("[");
        let iEnd = args.lastIndexOf("]");
        sInnerCom = args.slice(iStart+1,iEnd).join(" ");

        if (executable(sInnerCom) == true) {
            let pInnerPromise = await execute(sInnerCom, pChannel);
            pInnerPromise.then(result => { sInnerComResult = result });
        }

        // take all the elements of args that were used to encode the nested command
        // and replace them with the output we just got from that command
        // so any subsequent commands drawing from args will use it as an input string
        let throwaway = args.splice(iStart, iEnd-iStart+1, sInnerComResult);
    }

    let sComResult = "";
    switch(cmd){

        ...

        case "aut":
            if (args.length < 1) {
                // input string that should be in args actually isn't, so grab the content of the 2nd most recent message instead
                pMessages = await pChannel.fetchMessages({ limit: 2 });
                sComResult = com_aut([pMessages.last().content]);
                });
            } else {
                // input string is present in args, so just use that
                sComResult = com_aut(args);
            }
            break;
    }
    return sComResult;
}