You can pass the external date from a file to HQL. You can either manually store the date in a file or use a command like this:
$ date> date.txt
Then you have to pass this date.txt file which has the date, as the parameter to HQL. You can do it with the following syntax:
$ hive <path to hql file> -i <path to date.txt file>
$ hive "/home/user/sample.hql" -i "/home/user/date.txt"