The stored procedure sp_help_revlogin does not return a result set so it will not work with BCP. You will get an error message like "BCP host-files must contain at least one column" from BCP. The sp_help_revlogin uses the PRINT statement to output the T-SQL for creating logins.

You could use OSQL like in the example below.

declare @sql varchar(8000)

SELECT @sql = 'osql -E -S servername -q"exec [dbo].[sp_help_revlogin]" -o \\servername\f$\outputfilename.sql -w120 -n'

EXEC xp_cmdshell @sql