This php snippet creates a search provider description according to OpenSearch Description specification and displays a button for adding your site to users browser as new search engine. View demo at aam.ugpl.de.

Change "Your Site Name" in the following code snippet into the name fo your site and "Your Site Slogan" into a short description of your site.

<?php
/**
* This php snippet creates a search provider description
* and displays a button to add your site to your browser as new search engine
*
* Works with drupal 5.x, 4.7.x, 4.6.x and 4.5.x
*
* works for IE 7.+ and Mozilla Firefox 2.+
*
* Snippet submitted by aam
*/

global $base_url;
$site_name = variable_get("site_name", "drupal");

$xmlfile ="<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";
$xmlfile.="<OpenSearchDescription xmlns=\"http://a9.com/-/spec/opensearch/1.1/\">\n";
$xmlfile.="<ShortName>Your Site Name</ShortName>\n";
$xmlfile.="<Description>Your Site Slogan</Description>\n";
$xmlfile.="<Url type=\"text/html\"\n";
$xmlfile.="   template=\"".$base_url."?q=search/node/{searchTerms}\"\n";
$xmlfile.="/>  \n";
$xmlfile.="</OpenSearchDescription>\n";

if ( ! file_exists("files/opensearchprovider.xml") ) {
  if (!$fp = fopen("files/opensearchprovider.xml", "w")) {
			print "<br><b>Error: Cannot open XML file for search provider description</b>\n"; }
		else {
			// Write content to the opened file.
			if (!fwrite($fp, $xmlfile)) {
				print "<br><b>Error: Cannot write to XML file</b>\n";
				}
			else {
				print "<br><b>Success: XML file search provider description written</b>\n";}
				//print "<h3>Following XML file written:</h3>\n";
				//print "files/opensearchprovider.xml";
				//readfile ("files/opensearchprovider.xml");
			fclose($fp);
			}
  }

$output .= "<p><form>\n"; 
$output .= "<fieldset><legend><b>Add this site as search provider to your browser</b></legend>\n"; 
$output .= "<p>". t("Want to add %site as a new search provider? Just click the button below!", array("%site" => $site_name )) ."</p>\n";
$output .= "<p><form><INPUT TYPE=\"button\" VALUE=\"Add Search Provider\" onClick='window.external.AddSearchProvider(\"".$base_url."/files/opensearchprovider.xml\");'></form></p>\n";
$output .= "<noscript>\n";
$output .= "<p><b>". t("WARNING") .":</b>". t("JavaScript is disabled in your browser.");
$output .= t("The sidebar requires JavaScript support to be enabled.") ."</p>\n";
$output .= "</noscript>\n";
$output .= "</fieldset>\n"; 

print $output;
?>