PHP: Needing regex to camelCase a dashed/underscored string & test result against native PHP functions

I'm trying to streamline this method down. It basically takes in an action (string), makes dashed/underscored strings into camelCase and then tests if the result is equivalent to a native php function, if so it gets an underscore in front. I'm thinking all this could be one regex but I'm not sure how I'd test function_exists. Any help is greatly appreciated!

public function getMethod($action){
    if (strpos($action, '-') !== false){
        $action = str_replace(' ', '', ucwords(str_replace('-', ' ', $action)));
        $action = lcfirst($action);
    }

    if (strpos($action, '_') !== false){
        $action = str_replace(' ', '', ucwords(str_replace('_', ' ', $action)));
  开发者_开发知识库      $action = lcfirst($action);
    }

    // resolves native function names with underscore
    if (function_exists($action))  return "_".$action;
        else if ($action == 'list')  return '_list';
        else if ($action == 'new')   return '_new';
        else if ($action == '')  return 'index';
        else return $action;
}

After some more research and work I resulted with this:

public function getMethod($action){
    $pattern = array('/_(.?)/e', '/-(.?)/e', '/ (.?)/e');
    $action = preg_replace($pattern, 'strtoupper("$1")', $action);

    if (function_exists($action) || $action == 'list' || $action == 'new' || $action == 'sort')
        return '_'.$action;
    else if ($action == '')
        return 'index';
    else
        return $action;
}