TOPS-20 Commands Reference Manual

DEFINE

Establishes or cancels logical names for your job.

Format

@DEFINE (LOGICAL NAME) name:  list

where:

name:	is any combination of up to 39 alphanumeric characters that you want to use as a logical name. Use an asterisk (*) for this argument to withdraw all logical names. The colon after the logical name is optional.
list	is a series of devices, file structures, directories, file specifications, and/or other logical names; each item should be separated from the others by commas. Default - not specifying a list withdraws the logical name definition

Characteristics

Colon Designates a Logical Name

Normally, when you give a logical name to an EXEC command in the place of a file specification, structure, or directory name, a colon must follow the logical name. However, for the DEFINE and INFORMATION LOGICAL-NAMES commands, where the argument can only be a logical name, a colon after the logical name is optional.

Hints

DEFINE in LOGIN.CMD File

Your DEFINE command is valid for the current terminal session only. If there are logical names that you always want to use, put DEFINE commands into a LOGIN.CMD (or, for batch jobs started by SUBMIT commands within the control files of other batch jobs, a BATCH.CMD) file in your log-in directory.

Redefining System Logical Names

You can use the DEFINE command to redefine any system logical name for your own job. By repeating a system logical name in its own search list you expand its definition to include the other items, in the order you specify. Consider the system logical name SYS:, which is searched whenever you give a program name in place of a TOPS-20 command. If you redefine SYS: to be str:<directory>, SYS: you can run programs in str:<directory> by typing just their names. This will work as long as the program names are not the same as TOPS-20 commands.

Logical Names as Dummy File Specifications

You can use logical names as dummies for file specifications or devices when writing programs. Then, just before running such a program, use the DEFINE command to define these as real file specifications or devices, without changing the program itself.

More Information

For more information about using logical names, see the TOPS-20 User's Guide.

Special Cases

Using Recognition in the File Specifications

Normally, when you attempt to use recognition in a nonexistent filename, the system rings the terminal bell. However, for the DEFINE command, instead of ringing the terminal bell, the system may append part(s) of the default file specification, .0 or ..0, to the logical name definition. This is because DEFINE allows you to define a directory or file specifications that may not yet exist.

Note that a logical name definition that includes .0 or ..0 may not work for your use of the logical name; it is recommended that you specify the complete directory name or file specifications.

Restriction

Adding Comments to a DEFINE Command Line

You can add a comment to the end of any TOPS-20 command by preceding the comment with one of the comment characters: an exclamation point (!) or a semicolon (;). However, only the exclamation point can be used with the DEFINE command.

Using Short Logical Names Only

Although logical names can be up to 39 characters long and can include dollar signs ($), hyphens (-), and underlines (_), some commands and programs (such as programs originally written for the TOPS-10 operating system) accept a more limited set of logical names. These can be no more than 6 characters long and cannot include any special symbols. If all your logical names are of this kind, they will be acceptable to any TOPS-20 programs and commands.

Related Commands

INFORMATION LOGICAL-NAMES

for finding out the current definitions of logical names

Examples

Define a logical name for your job.

            @DEFINE LGN:  <MANUALS>, <SARTINI>

Withdraw the logical name.
```
            @DEFINE LGN:
```
Define a logical name to be a set of directories to which you have access. Then use the logical name to copy a file from one of them into your connected directory.
```
            @DEFINE MSM: <MANUALS>, <SARTINI>, <MCELMOYLE>
            @COPY MSM:4-UPED.TXT
             <MCELMOYLE>4-UPED.TXT.1 => 4-UPED.TXT.1 [OK]
```
Add one of your own directories to the definition of SYS: so that you can run .EXE files in that directory by typing just the program name.
```
            @DEFINE SYS: SYS:,AURORA:<WHITING.TOOLS>
```

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