To try this out see http://regexr.com?37i6s, or for a version which is less restrictive http://regexr.com/3e6m0.
Example JavaScript implementation:
var expression = /[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)?/gi;
var regex = new RegExp(expression);
var t="www.google.com";
if (t.match(regex)) {
alert("Successful match");
} else {
alert("No match");
}