Nodejs command line argument requires quotation marks to be recognized

I am new to node.js so please be gentle. I am trying to run a simple piece of code that converts rgb values to hex values. However, I can't seem to execute the program in the terminal without appending single quotation marks to my arguments.

When I type in:

 node index.js rgbhex rgb(255,255,255)

in my bash- terminal I am getting an error of:

 syntax error near unexpected token `(` 

However, when I do the following with single quotation marks around my arguments:

node index.js 'rgbhex' 'rgb(255,255,255)'

The code runs normally (i.e output is #ffffff). My question is why do I need to include the single quotation marks in my arguments? Any guidance is appreciated.

my index.js for reference :

function componentToHex(c) {
  var hex = c.toString(16);
  return hex.length == 1 ? "0" + hex : hex;
}

function rgbToHex(r, g, b) {
  return "#" + componentToHex(r) + componentToHex(g) + componentToHex(b);
}

//More comfortable solution

let red;
let green;
let blue;

if(process.argv[2]!=='rgbhex'){
red = Number(process.argv[2]);
green = Number(process.argv[3]);
blue = Number(process.argv[4]);

} else {
   let rgbInput = process.argv[3];
   let regexTest = /[0-9]+/g;
   let arrayOfRgbValues = rgbInput.match(regexTest);

   red = Number(arrayOfRgbValues[0]);
   green = Number(arrayOfRgbValues[1]);
   blue = Number(arrayOfRgbValues[2]);

} 
console.log(rgbToHex(red,green,blue));