There are 4 types of commands you can run at the SQL*Plus command line prompt:

1. SQL commands - Standard SQL statements to be executed on target database on the Oracle server. For example: "SELECT * FROM ggl_faq;" is a SQL command.

2. PL/SQL commands - PL/SQL statements to be executed by the Oracle server. For example: "EXECUTE DBMS_OUTPUT.PUT_LINE('Welcome to www.rendc.org')" runs a PL/SQL command.

SQL*Plus commands - Commands to be executed by the local SQL*Plus program itself. For example: "SET NULL 'NULL'" is a SQL*Plus command.

OS commands - Commands to be executed by the local operating system. For example: "HOST dir" runs an operating system command on the local machine.