Is it possible to customise the search engine buttons in GNOME Shell?

Gnome-Shell search providers are described by XML files in the folder /usr/share/gnome-shell/search_providers

You will notice two XML files - google.xml and wikipedia.xml

Lets create a new search provider - copy the google.xml file as a template

11.10

sudo cp /usr/share/gnome-shell/search_providers/google.xml /usr/share/gnome-shell/search_providers/duckduckgo.xml

12.04

sudo cp /usr/share/gnome-shell/open-search-providers/google.xml /usr/share/gnome-shell/open-search-providers/duckduckgo.xml

Now lets open the file and change some details to search with duckduckgo:

11.10

sudo nano /usr/share/gnome-shell/search_providers/duckduckgo.xml

12.04

sudo nano /usr/share/gnome-shell/open-search-providers/duckduckgo.xml

Change the following XML tags:

<ShortName>DuckDuckGo</ShortName>
<Description>DuckDuckGo Search</Description>
<Url type="text/html" method="GET" template="http://www.duckduckgo.com/?q={searchTerms}"/>

The only difficult part is finding out how a search engine searches - in duckduckgo I searched for something - you see in the title bar how the search provider adds its search terms

final result

In order to see the changes, you need to restart GNOME Shell by pressing Alt+F2, typing "r" and pressing enter.

Linked Questions:

1. Is it possible to re-arrange the search providers on the GNOME Shell Activities Overview display?

In case someone's interested in removing all search engines from the overlay screen, user asermax has published the Disable Search extension at the GNOME Shell Extensions website. Check it out: https://extensions.gnome.org/extension/203/disable-search/

It must be noted that this extension also removes the search bar at the top right corner of the overlay screen.