Overview of IDL Program Types

In addition to being a useful interactive data analysis tool, IDL is a powerful programming language. Many of IDL's programming language features and constructs can be used either interactively at the IDL command line or as part of a larger program — which can itself be invoked at the IDL command line or by other programs. A program may or may not be compiled before execution. The type of programs you use in IDL will depend upon your tasks.

Table 2-1: IDL Program Types
Program Type	Description
iTools State File (`.isv`)	Restore or share an iTools session — you can save the current state of an iTool as an iTools State (.`isv`) file. Whenever you close an iTool window, you are prompted to save the current state as an .`isv` file so that you can return to the current state of the data later when you open the .`isv` file. Other IDL users running the same version or a newer version of IDL can open .`isv` files. The iTool State file includes the data visualized at the time it was created. There is no need to provide a separate data file to support the visualization. See the iTool User's Guide for details.
$MAIN$ Program	Repeat a series of command line statements or interactively change variable values in a program file. These short programs or procedures are called $MAIN$ (main-level) programs. They are not explicitly named, and cannot be called from other programs. See Creating $MAIN$ Programs for details.
Named Program File (`.pro`)	Create programs and applications — you can create programs for data analysis or visualization using one or more named program files (*.pro). Program files are created in the IDL Editor or a text editor of your choice. See About Named Programs.
Batch File	Automate processing tasks — you can automate routine or lengthy processing tasks using a batch file, which contains one or more IDL statements or commands. Each line of the file is read and executed before proceeding to the next line. See Executing Batch Jobs in IDL for additional information on batch files.
SAVE File (`.sav`)	Share programs and distribute applications — you can create a SAVE file containing data or named program files in a `.sav` file to share with other users who may or may not have a full IDL installation. See Creating SAVE Files of Programs and Data for details.