Overview

OPEN VMS IS AN INTERACTIVE OPERATING SYSTEM, so it is not surprising that many of the programs written for it are also interactive. The dialog between a computer program and a user flows in two directions, from the program to the user and from the user to the program. Chapter 6 explained how to format and display output for the benefit of the user. This chapter discusses how to obtain input from the user.

A video terminal consists of an output device, the screen, and an input device, the keyboard. In addition to the process-permanent files SYS$OUTPUT and SYS$ERROR, which are used to write information to the screen, Open VMS maintains two process-permanent files from which input can be obtained. These files are accessed via the logical names SYS$COMMAND and SYS$INPUT. Exactly which files are accessed depends upon the current environment, as follows: See Sec.20.5, p.269

At the DCL prompt Both SYS$COMMAND and SYS$INPUT refer to the terminal keyboard.

During execution of an interactive procedure SYS$COMMAND refers to the terminal keyboard; SYS$INPUT refers to the procedure file.

During execution of a batch procedure Both SYS$COMMAND and SYS$INPUT refer to the procedure file.

At the DCL prompt or during interactive procedure execution, keyboard input can be obtained by reading from SYS$COMMAND. During batch procedure execution, there is no keyboard from which to obtain input.

11.1 The INQUIRE Command

The INQUIRE command is the simplest method of...