Webview, return output of bash -c

I'm calling runShellScript() as below. Can I make it return the bash output from echo? as it stands it doesn't appear to do this

		let shellScriptWrapper = {
			script: `echo "fff"`, 
			launchPath: '/bin/bash', 
			parameters: '-c',
			environmentVariables: '' 
		runShellScript( shellScriptWrapper )

It should be working but runShellScript returns a promise. Here is an example from the docs:

async function runSomeShellScriptScript() {

// put the shell script into a string (single backticks are great for multiline strings)
let shellScript = `echo "hello world"`;

let shellScriptWrapper = {
    script: shellScript, // mandatory
    launchPath: '/bin/bash', //optional - default is /bin/bash
    parameters: '-c', // optional - default is -c
    environmentVariables: '' //optional e.g. VAR1=/test/;VAR2=/test2/;

// this will execute the Shell Script and store the result in the result variable.
let result = await runShellScript(shellScriptWrapper);

//do whatever you want with the result
console.log('result', result);