The built-in packages offer a number of ways to generate output from within your PL/SQL program. While updating a database table is, of course, a form of “output” from PL/SQL, this chapter shows you how to use two packages that explicitly generate output. UTL_FILE reads and writes information in server-side files, and DBMS_OUTPUT displays information to your screen.
DBMS_OUTPUT provides a mechanism for displaying information from your PL/SQL program on your screen (your session’s output device, to be more specific). As such, it serves as just about the only immediately accessible (meaning “free with PL/SQL”) means of debugging your PL/SQL stored code. It is certainly your “lowest common denominator” debugger, similar to the used-and-abused MESSAGE built-in of Oracle Forms. DBMS_OUTPUT is also the package you are most likely to use to generate reports from PL/SQL scripts run in SQL*Plus.
Of all the built-in packages, the DBMS_OUTPUT package (and its PUT_LINE procedure, in particular) is likely to be the one you will find yourself using most frequently. You may therefore find it strange that I never call DBMS_OUTPUT.PUT_LINE. I find the design and functionality of DBMS_OUTPUT to be substandard and very frustrating.
In fact, I recommend that you never use this package—at least, not directly. You should instead encapsulate calls to DBMS_OUTPUT (and the PUT_LINE procedure, in particular) inside a package ...