Add a new button ribon with csom

Question

I'm trying to add a new button in my sharepoint 2013 server via csom because in a few months I'll pass to project online and wsp aren't support anymore by project online So I found this guide on the net: https://www.c-sharpcorner.com/article/custom-actions-using-csom-for-sharepoint-online-part-2/

But when I have to add this line:

PublishRibbonaction.CommandUIExtension = @ 
"<CommandUIExtension><CommandUIDefinitions>" + 
"<CommandUIDefinition Location=\"Ribbon.Documents.Copies.Controls._children\">" + 
"<Button Id=\"InvokeAction.Button\" TemplateAlias=\"o1\" Command=\"EditFormButtonCommand\"
  CommandType=\"General\" LabelText=\"CustomListRibbonAction\"
  Image32by32=\"_layouts/15/images/placeholder32x32.png\"
  Image16by16=\"_layouts/15/images/placeholder16x16.png\" />" +
"</CommandUIDefinition>" + 
"</CommandUIDefinitions>" + 
"<CommandUIHandlers>" + 
"<CommandUIHandler Command =\"EditFormButtonCommand\" CommandAction =\
"javascript:OpenPopUpPageWithTitle(
 'https://tarundev.sharepoint.com/sites/sharepointmates/_layouts/15/viewlsts.aspx',
  RefreshOnDialogClose, 600, 400,'CustomList Ribbon');\" EnabledScript=\"javascript: 
  SP.ListOperation.Selection.getSelectedItems().length >= 1\" /> " + "
</CommandUIHandlers>
</CommandUIExtension>";

(I replaced the sharepoint URL by mine) I have the following error message:

Keyword, identifier, or string expected after verbatim specifier: @ Invalid expression term ''

Any idea of what I'm doing wrong?

Answer 1

Remove the @ sign. You are not using it anyway. If you want to use it, it should go with the string to which it is applied so @"<CommandUIExtension><CommandUIDefinitions>" (i.e. not on a different line), but that particular string doesn't have anything on it requiring the @ sign (i.e. all the @ sign does is cause \ not to be treated as an escape sequence, but you don't have any \ in that string so it's not needed, and removing the @ will fix the compiler error).