Find port number of a SQL instance using TSQL

DECLARE @portNumber varchar(20), @key varchar(100)

if charindex('\',@@servername,0) <>0
begin
set @key = 'SOFTWARE\MICROSOFT\Microsoft SQL Server\' +@@servicename+'\MSSQLServer\Supersocketnetlib\TCP'
end
else
begin
set @key = 'SOFTWARE\MICROSOFT\MSSQLServer\MSSQLServer\Supersocketnetlib\TCP'
end
EXEC master..xp_regread @rootkey='HKEY_LOCAL_MACHINE', @key=@key, @value_name='Tcpport', @value=@portNumber OUTPUT
SELECT 'Server Name: '+@@servername + ' Port Number:'+convert(varchar(10),@portNumber)