Before Release 2 of Oracle 9i it was necessary to enter all OS-Directories in the init.ora file and restart the instance if you needed to change those directories. From 9iR2 the UTL_FILE package has been enhanced to allow the dynamic changing of directories without bouncing the instance and without loosing any of the needed restrictions for user/schema access to this facility. For full details on how to now use this package check out this article on the OTN.
For further examples you may also want to consult this earlier document on using the new features.
Leave a comment