how to get current username when running a workflow ?

Here is what I would like to do:

Say each user is allowed to have 4 QA instances, create a workflow, when a user run it from vCenter plugin, it should be able to get the user's SSO username jsmith, then it will query if there is a existing VM jsmith_qa1,jsmith_qa2,jsmith_qa4, etc, if there isn't one, then create one for him; otherwise tell the user he already has 4 instances.

I found I can use getCurrentLdapUser to do get jsmith@domain.name , now I want to remove the domain.name ( there are mulitple domains ) :

username = actionResult.userPrincipalName.replace("@[a-z.]+","");

This doesn't seem work. Does anyone know where I can find good document for vRealize Orchestrator scripting document?

Thanks!

Jack