Find OS User for command shell spawn from SQL Server context

If the policy on the server allows execution of xp_cmdshell then can find out the windows user that owns the spawned shell to handle OS commands executed from within sql server context

   EXEC xp_cmdshell 'whoami'

to get the value into a variable can do following

   DECLARE @whoisit nvarchar(4000)
   CREATE TABLE #test ( output nvarchar(4000) null )

   INSERT INTO #test (output)
   EXEC xp_cmdshell 'whoami'

   SELECT top 1 @whoisit = output 
     FROM #test 
    WHERE output IS NOT NULL

   SELECT @whoisit "whoisit"

   DROP TABLE #test