GetUsername.php

<?php

if (!defined('MEDIAWIKI')) {
	die('This file is a MediaWiki extension, it is not a valid entry point');
}

$wgExtensionCredits['parserhook'][] = array(
	'name' => 'GetUserName',
	'version' => '1.0',
	'url' => 'https://www.mediawiki.org/wiki/Extension:GetUserName',
	'author' => 'Ejcaputo',
	'description' => "Allows the current user's name to be put in a page"
);

$wgHooks['ParserFirstCallInit'][] = "ExtGetUserName::setup";
$wgHooks['LanguageGetMagic'][] = 'ExtGetUserName::languageGetMagic';
class ExtGetUserName
{
	private static $parserFunctions = array(
		'USERNAME' => 'getUserName',
	);

	public static function setup(&$parser)
	{
		// register each hook
		foreach (self::$parserFunctions as $hook => $function)
			$parser->setFunctionHook($hook,
				array(__CLASS__, $function), SFH_OBJECT_ARGS);

		return true;
	}

	public static function languageGetMagic(&$magicWords, $langCode)
	{
		$magicWords['USERNAME'] = array(0, 'USERNAME');
		return true;
	}

	public static function getUserName(&$parser, $frame, $args)
	{
		$parser->disableCache();
		global $wgUser;
		return trim($wgUser->getName());
	}
}