MTB Statements

Logical Unit Number

A logical unit number (lun) is the numeric value that is assigned to an I/O device, data file, printer, spooler, gateway, etc. by an OPEN statement. The lun may be a numeric constant, numeric variable, or a symbolic constant. Its value may be from 0 through 49. This parameter appears in input/output statements.

In a foreground partition, lun 0 is opened (by the QMONITOR program) and assigned to the video screen. Thus luns 1 through 49 are available for data files, printers, spoolers, gateways, etc.

In a background partition, lun 0 is not opened by QMONITOR, as there is no video screen associated with a background partition.

Logical unit number assignments are concluded with the CLOSE statement.

Example 1:
PRINT (0) "HELLO WORLD"
In this example, the message "HELLO WORLD" is displayed on logical unit number 0 (the video screen).

Example 2:
OPEN (1) "LP1" . PRINT (1) "CUSTOMER MASTER LISTING" . CLOSE (1)
In this example, logical unit number 1 is associated with the printer named LP1. This association is established with the OPEN statement, then used via the PRINT statement, and finally concluded with the CLOSE statement.

Example 3:
1000 FORMAT CUSTNUM$;NAME$;ADDRESS$;CITY$;STATE$;ZIP$ OPEN (5) "CUSTFILE" . READ (5,1000) KEY=CUSTNUM$ . CLOSE (5)
In this example, logical unit number 5 is associated with the data file named "CUSTFILE." This association is established with the OPEN statement, then used via the READ statement, and finally concluded with the CLOSE statement.

Example 1:	PRINT (0) "HELLO WORLD" In this example, the message "HELLO WORLD" is displayed on logical unit number 0 (the video screen).
Example 2:	OPEN (1) "LP1" . PRINT (1) "CUSTOMER MASTER LISTING" . CLOSE (1) In this example, logical unit number 1 is associated with the printer named LP1. This association is established with the OPEN statement, then used via the PRINT statement, and finally concluded with the CLOSE statement.
Example 3:	1000 FORMAT CUSTNUM$;NAME$;ADDRESS$;CITY$;STATE$;ZIP$ OPEN (5) "CUSTFILE" . READ (5,1000) KEY=CUSTNUM$ . CLOSE (5) In this example, logical unit number 5 is associated with the data file named "CUSTFILE." This association is established with the OPEN statement, then used via the READ statement, and finally concluded with the CLOSE statement.