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VMS Symbols & Logical Names

This is a large topic that cannot be covered adequately in this lecture. A full understanding of VMS symbols and logical names is useful, but not essential in order to use the Alpha and GCG effectively. This lecture and lab session will provide a short summary of symbols and logicals and pointers to resources that will enable you to learn more if that becomes necessary for your work.

A. What are VMS Symbols?

***Symbols are shorthand names or aliases referring to DCL (Digital Command Language) commands on the Alpha.

***In general DCL commands are entered at the "$" prompt in order to give instructions to the VMS operating system.

***Symbols are often assigned to a command plus one or more parameters and/or qualifiers.

***For example the symbol "GOWORK" is equivalent to the command:

***Another example is the symbol "DIR" meaning:

***Effectively used, symbols can greatly simplify using the Alpha. They can reduce typing time and typing errors by specifying frequently used commands with short names that are easier for you to type. They can also help you to remember commands by assigning names that make sense to you.

***Many symbols are defined by the system or by GCG at the time of login.
***An example of a system-defined symbol is EVE , which is equivalent to: EDIT/TPU

***Examples of GCG symbols are UP , DOWN , and OVER , which provide an easier way to move around between directories without using the square brackets [ ] that VMS requires.

***Multiple symbols can mean the same thing. For example, the symbols M , MA , MAI , and MAIL could all equate to:
***Symbols can also be used to define other character strings, such as character or numeric values

***Use the command SHOW SYMBOL to show symbols defined in your global symbol table.
At the $ prompt, type SHO SYM , then at the _Symbol: prompt, type the name of the symbol you wish to see.
If you type *.* you will see a VERY long list.
***New symbols can be defined at the command line using the syntax:
$ symbol-name :== DCL command/MOD 
  • The symbol-name is the shorthand name or alias that you want to type.

  • The DCL command/MOD is the actual name of the command, with all of the qualifiers and parameters that you want to include.

***Symbols crated on the command line will only last for the current login session. To create a permanent new symbol, you must add the symbol definition to your LOGIN.COM file. We will discuss this further in the lab session.

B. What are VMS logical names?

***Logicals are shorthand names or aliases referring to files, directories, disks, executable files and other DCL entities on the RCR's Alpha server.

***Logicals can reduce typing by allowing you to specify files and directories that you refer to frequently with names that are easier to type and to remember. They can also help you reduce confusion about where files are stored.

***Some logicals are defined by the system or by GCG at the time of login.

***Examples of system logicals are SYS$APPLE and SYS$USER , which refer to the locations of the home directories of most RCR users.

***GCG logicals include the names of the different taxonomic sections of the GenBank nucleic acid database, such as PLANT , PRIMATE , RODENT , and RNA

***Multiple logical names can point to the same thing. For example, PR , PRI , GB_PR , and PRIMATE all refer to the GenBank primate sequences.

***To see what a logical actually means, at the $ prompt, type:
$ SHOW LOGICAL {logical-name }
***Watch out: If you type "SHO LOG" without specifying a filename, you will get a VERY long list.

***Any user can define logicals while logged into the Alpha.

*** For temporary use during a login session, define the logicals at the $ prompt.

*** Use the DEFINE command to define a logical name for temporary use during one login session only:
$ DEFINE  logical-name  equivalence-name 
  • The logical-name is the shorthand name or alias that you want to use
  • The equivalence-name is the actual name of the object

***For permanent use, logicals should be defined in the LOGIN.COM file so that they are defined automatically during each login and available for use at all times.

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Using Computers for Molecular Biology
Stuart M. Brown, Ph.D, RCR, NYU Medical Center
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