simple-string-template.nut

//{!first_name}

function fillTemplate(tpl, data)
{
	local missing_keys = [];
	local result = tpl.gsub(
		"{!%s*(%S[^%s}]+)%s*}",
		function(key)
		{
			if(key in data)
			{
				return data[key];
			}
			missing_keys.append(key);
			return key;
		}
	);
	if(missing_keys.len()) result = missing_keys;
	return result;
}

local result = fillTemplate("Hello {!first_name} - I hope everything is going well with you {!first_name}", {"first_name" : "Mike"});
if(type(result) == "array")
{
	print("missing keys on data :", result.join(", "));
}
else print(result);