xdg-settings_command_examples
xdg-settings – get various settings from the desktop environment
Get the desktop file name of the current default web browser
xdg-settings get default-web-browser
Check whether the default web browser is firefox.desktop, which can be false even if “get default-web-browser” says that is the current value (if only some of the underlying settings actually reflect that value)
xdg-settings check default-web-browser firefox.desktop
Set the default web browser to google-chrome.desktop
xdg-settings set default-web-browser google-chrome.desktop
Set the default mailto URL scheme handler to be evolution.desktop
xdg-settings set default-url-scheme-handler mailto evolution.desktop