// ==UserScript==
// @include     http://www.google.*/
// @include     http://www.google.*/search*
// @include     http://www.bing.com/
// @include     http://www.bing.com/search*
// @include     http://www.yahoo.com/
// @include     http://search.yahoo.com/search*
// ==/UserScript==

document.querySelector('input[name=q], input[name=p]').value = "  -w3schools";