Updated: 11 December 1998

OpenVMS User's Manual

DCL (DIGITAL Command Language) is a set of English-like instructions that tell the operating system to perform specific operations. DCL provides you with over 200 commands and functions to use in communicating with the operating system to accomplish computing tasks.

1.3.1 Usage Modes

You can use DCL in the following two modes:

• Interactive
  In interactive mode, you enter commands from your terminal. One command has to finish executing before you can enter another.
• Batch
  In batch mode, the system creates another process to execute commands on your behalf. A batch job is a command procedure or program that is submitted to the operating system for execution as a separate user process. After you submit the command procedure for batch execution, you can continue to use your terminal interactively.
  Batch jobs and network processes use DCL in batch mode. See Chapter 18 for more information about processes.

When you enter a DCL command, it is read and translated by the DCL interpreter. The way the command interpreter responds to a command is determined by the type of command entered. The three types of DCL commands are as follows:

• Built-in commands
  These commands are built in to the DCL interpreter and are executed internally.
• Commands that invoke programs
  DCL calls another program to execute the command rather than executing it internally. The program invoked to execute a command is referred to as a command image. This command image can be either an interactive program, a utility (such as Mail), or a noninteractive program (such as COPY).
• Foreign commands
  A symbol that executes an image is referred to as a foreign command. A foreign command executes an image whose name is not recognized by the command interpreter as a DCL command. Refer to Chapter 14 for complete information on symbols.

DCL, like any language, has its own vocabulary and usage rules. The vocabulary consists of commands, parameters, and qualifiers, which are put together in a way that DCL can interpret. The way in which the parts of a command line are put together is referred to as the command line syntax.

A DCL command line uses the following format:

[$] command [[/qualifier[=value]]...] [[parameter[=value][/qualifier...]]...]

For a complete description of the components of a DCL command line, see Section 3.2.

Lexical functions are command language constructs that the DCL interpreter evaluates and substitutes before it interprets a command string. Chapter 17 discusses lexical functions in more detail.

1.4 Files and Directories

A file is a system object that contains information. This information can be machine-readable data that the computer understands. It can also be text you enter and manipulate. The text in the file might be the text of a document, a program, or a list of addresses. You can examine the data in these files by displaying the files on a terminal screen or by printing them on paper.

Chapter 4 describes how to create and organize files to store information.

A directory is a special kind of file that contains the names and locations of files; files are listed in directories. For example, when the system manager creates a user account for you (see Section 1.1), you automatically have a directory with the same name as your user name. If your user name is JONES, the directory is [JONES].

Chapter 5 describes how to use directories to organize and manage files.

Directory files are stored on disks. Disks are one type of hardware device that the operating system uses to store information.

1.4.1 File Specifications

Every file must have a file name or file type to identify it to both the system and you. A file also has a version number. You can have several versions of a file. Unless you specify a version number, the system uses the highest existing version number of a file. When you edit a file, the system saves the original file and produces a modified output file. By default, the output file has the same name and type as the original but the version number is incremented by one.

The file name, file type, and version number form a file specification. A full file specification:

• Completely describes the access path the system uses to locate and identify a file
• Can include the directory in which the file is located and the network node on which the file resides
• Is also known as a network file specification

Each disk contains a main directory, which can be set up by a system manager or by the system itself. This main directory is called the master file directory (MFD) and contains a list of user file directories (UFDs). UFDs are files in the master file directory that point to top-level directories. Your top-level directory is usually your login or default directory. Unless your account has been modified to do otherwise, the system automatically places you in your top-level directory when you log in.

In most cases, a UFD exists for each user on the system. It contains the names of and pointers to files cataloged in a user's directory. Chapter 5 contains more information about directory structures.

1.4.3 Subdirectories

A subdirectory is a directory file within another directory or subdirectory file. Subdirectories let you organize files into meaningful groups. For example, you might have one subdirectory that contains memos and another subdirectory for status reports.

Like a directory, a subdirectory contains names and pointers for the files cataloged within it. A subdirectory can contain an entry for another subdirectory, which can contain an entry for another subdirectory, and so on. This structure (a top-level directory plus subdirectories) is called a hierarchical directory structure. In a typical environment, the maximum number of subdirectories possible is seven.

1.5 OpenVMS Utilities

The following sections provide an overview of some basic OpenVMS utilities described in this manual.

1.5.1 Mail and MIME Utilities

The OpenVMS Mail utility (MAIL) lets you send messages to and receive messages from other users on your system or on any computer connected to your system by DECnet software.

As a complement to MAIL, the MIME utility allows you to encode and decode MIME-encoded messages that you have received from other users or that you want to send to yourself.

Chapter 6 describes how to use Mail and the MIME utility.

1.5.2 Phone Utility

The OpenVMS Phone utility (PHONE) lets you communicate with other users on your system or on any computer that is connected to your system by DECnet software.

Chapter 7 describes how to use Phone.

1.5.3 Text Editors

Text editors allow you to create and modify text files. With a text editor, you can enter text from a keyboard and modify the text using text editing commands. For example, you can type in data for a report and then rearrange sections, duplicate information, substitute phrases, or format text. You can use text editors to create and modify source files for programming languages (such as DEC C for OpenVMS or VAX BASIC) or text formatters (such as VAX DOCUMENT or DIGITAL Standard Runoff). The operating system supports several text editors. Chapter 8 describes how to use EVE, and Chapter 9 describes how to use EDT.

1.5.4 DIGITAL Standard Runoff (DSR)

DIGITAL Standard Runoff (DSR) is a text formatter that processes source files into formatted text and intermediate files, and creates tables of contents and indexes. You use a text editor to create a source file, to which you should give the file type .RNO. This file contains text, DSR formatting commands, flags (special instruction characters you insert), and control characters.

Chapter 10 describes how to use DSR and lists DSR commands.

1.5.5 Sort/Merge Utility

The OpenVMS Sort/Merge (SORT/MERGE) utility can be invoked in two ways: by using the SORT command or by using the MERGE command. When you invoke the Sort/Merge utility with the DCL command SORT, it sorts records from one or more input files, according to the fields you select, and generates one reordered output file. You can use the Sort/Merge utility to reorder records in a file (or files) so that they are in alphabetic or numeric order and either ascending or descending order.

When you invoke the Sort/Merge utility with the DCL command MERGE, it combines up to 10 previously sorted files into one ordered output file.

For information about using the Sort/Merge utility, see Chapter 11.

1.6 Devices

The following sections provide an overview of devices you can use in an OpenVMS environment.

1.6.1 Mass Storage Devices

Mass storage devices, such as disks and magnetic tapes, save the contents of files on a magnetic medium. Files saved this way can be accessed, updated, modified, or reused at any time.

1.6.2 Record-Oriented Devices

Record-oriented devices, such as terminals, printers, mailboxes, and card readers read and write only single physical units of data at a time and do not provide online storage of the data. (Printers and card readers are also called unit-record devices.)

1.6.3 Disks and Magnetic Tapes

The files you commonly access are stored on disks or magnetic tapes. Your user file directory (UFD) and your default directory with all your files and subdirectories are located on a disk. You can use a file specification that contains directory information only if the file is located on a disk. Magnetic tapes do not have directory structures. To obtain a file stored on tape, use a file specification that contains only file information.

Chapter 5 describes how to access files that are not on your default device. Chapter 12 describes how to use private volumes, which are tape and disk devices that are not available systemwide.

1.7 Logical Names

A logical name is a name equated to an equivalence string or to a list of equivalence strings. When you define a logical name, you equate one character string to an equivalence string, which is usually a full or partial file specification, another logical name, or any other character string. Once you equate a logical name to one or more equivalence strings, you can use the logical name to refer to those equivalence strings. For example, you might assign a logical name to your default disk and directory. Logical names serve two main functions: they increase readability and file independence.

Chapter 13 contains information about logical name tables and describes how to use logical names.

1.7.1 Readability

You can define commonly used files, directories, and devices with short, meaningful logical names. Such names are easier to remember and type than the full file specifications. You can define names that you use frequently in your login command procedure. A system manager can define names that most users on your system use frequently in the site-specific system startup command procedure.

1.7.2 File Independence

You can use logical names to keep your programs and command procedures independent of physical file specifications. For example, if a command procedure references the logical name ACCOUNTS, you can equate ACCOUNTS to any file on any disk before executing.

1.8 Symbols

Symbols are names that represent numeric, character, or logical values. When you use a symbol in a DCL command line, DCL uses the value you assign to the symbol. By defining a symbol as a command line, you can execute the command by typing only the symbol name.

Entering DCL command lines that include parameters, multiple qualifiers, and values can make for much typing and can be time-consuming. To simplify your interaction with DCL and to save time, you can establish symbols to use in place of command names and entire command strings you type frequently.

You can also use symbols in command procedures to collect, store, and manipulate certain types of data.

Chapter 14 describes how to use symbols in DCL commands and command procedures.

1.9 Command Procedures

A command procedure is a file that contains a series of DCL commands. Some simple command procedures might contain only one or two DCL commands; complex command procedures can function as sophisticated computer programs. When a command procedure is executed, the DCL interpreter reads the file and executes the commands it contains.

1.9.1 System Login Command Procedures

If your system manager has set up a system login command procedure, it is executed when you log in. A system login command procedure lets your system manager ensure that certain commands are always executed when you and other users on the system log in.

1.9.2 Personal Login Command Procedures

After executing the system login command procedure, the system executes your personal login command procedure, if one exists. Your personal login command procedure lets you customize your computing environment. The commands contained in it are executed every time you log in. When you log in, the system automatically executes up to two login command procedures (the systemwide login command procedure and your own login command procedure, if it exists).

The person who sets up your account might have placed a login command procedure in your top-level directory. If a login command procedure is not in your top-level directory, you can create one yourself, name it LOGIN.COM and place it in your top-level directory. Unless your system manager tells you otherwise, the LOGIN.COM file that you create will be executed when you log in. A sample personal login command procedure is included in Chapter 15. Appendix C contains several complete command procedures.

1.10 Lexical Functions

Lexical functions return information to a command line or command procedure. The information returned can be about your process, the system, files and devices, logical names, strings, or data types. Lexical functions are identified by the prefix F$.

You can use lexical functions in any context in which you normally use symbols or expressions. In command procedures, you can use lexical functions to translate logical names, to perform character string manipulations, and to determine the current processing mode of the procedure.

Chapter 17 describes how to use lexical functions to obtain and manipulate information within a command procedure.

1.11 Processes and Programs

A process can be a detached process (a process that is independent of other processes) or a subprocess (a process that is dependent on another process for its existence and resources). Your main process, also called your parent process, is a detached process.

Chapter 18 describes how to use processes to perform computing tasks.

A program, also called an image or an executable image, is a file that contains instructions and data in machine-readable format. Some programs are associated with and invoked by a DCL command. For example, when you type the DCL command COPY, the system executes the program SYS$SYSTEM:COPY.EXE. Some programs are invoked by entering the DCL command RUN followed by the program name.

1.11.1 User Authorization Files (UAFs)

The system obtains the characteristics that are unique to your process from the user authorization file (UAF). The UAF lists those users permitted to access the system and defines the characteristics for each user's process. The system manager usually maintains the UAF. It is within your process that the system executes your programs (also called images or executable images) one at a time.

1.11.2 Creating Image Files

Image files can be supplied by the operating system or by you and usually have the other window file type .EXE. You cannot examine an image file with the DCL commands TYPE, PRINT, or EDIT because image files do not consist of ASCII characters. (Text files contain ASCII characters, which are a standard method of representing the alphabet, punctuation marks, numerals, and other special symbols.)

Chapter 18 contains more information about using programs.

1.12 System Security

Each system site has unique security requirements. For this reason, every site should have a system security policy that outlines physical and software security requirements for system managers and users. The OpenVMS Guide to System Security describes the security features available with the operating system and the tasks that system managers can perform to maintain account and system security.

Chapter 2 describes password management and account security. Chapter 4 and Chapter 5 describe how users can protect their files and directories from unauthorized access.

1.12.1 Protected Objects

To ensure system security, the OpenVMS operating system controls both access to the system and access to any object that contains shareable information. These objects, such as devices, volumes, logical name tables, files, and queues, are known as protected objects. All protected objects list a set of access requirements that specify who has a right to access the object in a given manner.

Chapter 19 describes general security issues such as controlling access to protected objects and accessing data on remote systems.

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