How can I access the "selected_text" variable from Shell script?

Here is a fully working script, which uses the say command to speak the selected text:

(async ()=> {

let selectedText = await callBTT('get_string_variable', {variable_name:'selected_text'})


// put the shell script into a string (single backticks are great for multiline strings)
let shellScript = `say ${selectedText}`;


let shellScriptWrapper = {
    script: shellScript
 
};


let result = await runShellScript(shellScriptWrapper);
returnToBTT(result)


})();