Open Procedures 

The three OPEN procedures open a specified file for input and/or output.

· OPENR (OPEN Read) opens an existing file for input only.

· OPENW (OPEN Write) opens a new file for input and output. If the file exists, it is truncated and its old contents are destroyed.

· OPENU (OPEN Update) opens an existing file for input and output.

Calling Sequence

OPENR, Unit, File [, Record_Length]
OPENW, Unit, File [, Record_Length]
OPENU, Unit, File [, Record_Length]


Unit The unit number to be associated with the opened file.
File A string containing the name of the file to be opened.

The procedures have keyword parameters that enable them to be customized for particular purposes and operating platforms. See IDL Online Help for details.