Command Languages

Command Languages originated with operating system commands. They are distinguished by their immediacy and by their impact on devices or information. Users enter a command, watch what happens, and based on the result enter the next command.

Command Languages are distinguished from menu selection in that the user must remember syntax and initiate action. With menu selection the user is presented a limited number of choices and prompted to choose from among them. Menu selection, therefore, is more response than initiative.

Command language users often are burdened with having to memorize complicated syntax. It may not be obvious, for example, that the purpose of the following Unix command is to delete blank lines from a file:

grep -v ^$ file1 > file2

Even the more ubiquitous MS-DOS can be a bit confusing. A common error is mistaking when to use the forward slash and when to use the backslash.

BACKUP C:\*.* A: /S/M

More Operating System Command Language Examples

IBM JCL

//GO.TAPEFILE DD DSN=TEST.ISAM.CREATE,UNIT=TAPE,
// VOL=SER=4356,DISP=(OLD,KEEP)
//GO.ISAMFILE DD DSN=NEW.ISAM.FILE,UNIT=3300,
// VOL=SER=TEST,DISP=(,CATLG,DELETE),
// DCB=DSORG=IS,SPACE=(CYL,(5))

IBM OCL

// LOAD PROG5
// FILE NAME-EXCHANGE,DISP-SHR
// FILE NAME-CMASTR,LABEL-MASTER,DISP-OLD
// FILE NAME-TRADECH,DISP-NEW
// RUN

OpenVMS DCL

$ SET DEFAULT WORKDISK:[SALES.DATA]
$ ASSIGN/USER REPORT.LIS SYS$OUTPUT
$ RUN SALESREPORT
$ PRINT/COPIES=2 REPORT.LIS
$ DELETE REPORT.LIS;

Unix Shell Commands

Unix Shell commands are often perceived as being somewhat cryptic. One reason is that Unix shell commands (unlike, for example, VMS DCL commands) may not be abbreviated. Therefore, they were designed to be short to minimize keystrokes. However, the commands often are not named to represent their function. So, while you might rather quickly pick up that "rm" means remove a file, and "cp" means copy a file, you might have a more difficult time with "biff."

Most Unix systems can notify you of incoming mail messages while you are logged in by displaying a "You have new mail" message to your terminal screen. The biff command toggles this capability on and off. The command biff y allows the new mail notification to be displayed; the command biff n suppresses it.

Why "biff" you ask? The command was written by a Berkeley grad student whose dog, Biff, used to bark at the mailman.