InfoPath Dev

Hi all, When a user lands on my SharePoint 2013 landing page in my organisation, they're landing on it as they need to fill out a InfoPath requirements form. Part of the form has a calculated value to show the requester, (I've used the 'Modified By' field) this will be used for when the user submits the form, it will automatically pick this field as the person to reply too. However, the form hasn't been submitted yet, so I can't really use the 'Modified By' field. So what field do I use in order to ascertain the user who has access the form in the first place? Hope that makes sense. Thanks, Jon

Looking at another post, I can see how to put the current user who is submitting the form, however the form has the following on there: 'i:0#.f|membership|[email protected]' How do I get rid of the text before the email address? Thanks, Jon

Use substring-before. Syntax would be like: substring-before(userName(), "i:0#.f|membership|")