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DEFINE command

The DEFINE command 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

     1.  Define a logical name for your job.

         @DEFINE LGN:  <MANUALS>, <SARTINI>

     2.  Withdraw the logical name.

         @DEFINE LGN:

     3.  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]

     4.  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>