|Document revision date: 30 March 2001|
This chapter describes how to use the DIGITAL Command Language. This chapter includes information about:
For additional information, refer to:
The DIGITAL Command Language (DCL) is a set of English-like instructions that tell the operating system to perform specific operations.
DCL commands let you do the following:
To enter a DCL command, type the command at the DCL prompt ($) and press Return. DCL is not case sensitive; you can enter commands in either uppercase or lowercase letters.
In the following example, the DCL command SHOW TIME is entered as follows:
$ SHOW TIME [Return]
The system responds by displaying the current date and time and returns the DCL prompt to indicate it is ready to accept another command:
11-DEC-1999 15:41:43 $
The following table lists the DCL commands you use to perform a few common computing tasks:
|COPY||Makes a copy of a specified file|
|COPY/FTP||Transfers files between hosts over a TCP/IP network|
|CREATE||Creates files or directories|
|DELETE||Erases a specified file and removes it from a directory|
|DIRECTORY||Displays the contents of a directory (list of files)|
|EDIT||Views and changes the contents of a text file|
|LOGOUT||Ends your session|
|Sends a specified file to a printer for printing|
|RENAME||Changes the name or the location of a specified file|
|SET||Controls how you see the system on the screen|
|SHOW||Displays the status of the system|
|TYPE||Displays the contents of a specified file on the screen|
In addition to these DCL commands, you can perform tasks by using specific key sequences. A key sequence is a shortcut or a way to get the system's attention while it is processing another command.
To enter a key sequence, hold down the Ctrl key while you press and release a second key.
The following table describes a few commonly used key sequences. (Additional key sequences are listed in Section 3.11.)
|Ctrl/C||During command entry, cancels command processing. Ctrl/C displays on your screen as Cancel.|
|Ctrl/Y||Interrupts command processing. Ctrl/Y displays on your screen as Interrupt.|
|Ctrl/T||Displays information about the current process, unless the system is temporarily unresponsive or is set to NOBROADCAST. For more information on using Ctrl/T, see Section 2.9.|
Like a spoken language, DCL is made up of words (vocabulary) and word order (syntax or format). The following sections describe these two elements and explain how to construct a valid DCL command.
The following example shows the general format and parts of a DCL command line:
The following list describes each element of the DCL command line:
The following items may also be used in a DCL command line:
If you are working in an environment with Extended File Specifications, refer to the OpenVMS Guide to Extended File Specifications for information about using wildcard syntax in DCL commands.
Just as a spoken language depends on the order of words to create meaning, DCL requires that you put the correct elements of the command line in a specific word order or format.
Following are two examples of the syntax, or format, used for typical DCL commands:
3.3 Entering DCL Commands
When you enter a DCL command, some parameters are required; they must be entered on the command line. If you do not enter them, the system prompts you to supply the missing information. A line beginning with an underscore (_) means that the system is waiting for your response.
When you are prompted for an optional parameter, press Return to omit it. At any prompt, after you enter the required parameter, you can enter one or more of the remaining parameters and any additional qualifiers.
Note that you must enclose in quotation marks ("") any parameter containing a slash (/) or at sign (@).
In the following example, the TYPE command requires a file specification. Because a file specification is a required parameter of the TYPE command, if you do not enter one, the system requests it.
$ TYPE _File: WATER.TXT
If you press Ctrl/Z after a command prompt, DCL ignores the command and
redisplays the DCL prompt.
3.3.2 Using Defaults
Some items, called defaults, need not be specified on the command line. When DCL performs an operation by default, it assigns a command certain values or performs certain functions associated with that command even though you may not have explicitly specified those values or functions when you entered the command. In general, the values and functions are those considered typical or expected by users.
DCL supplies default values in several areas, including command parameters and qualifiers. For parameter defaults, see the sections in this manual that describe the specific DCL command. Qualifier defaults are described in Section 3.6.
If the number of copies is not specified as a qualifier for the PRINT command, DCL uses the default value 1. In the following example, the default is overridden and multiple copies of the file are printed by including the /COPIES qualifier on the PRINT command line:
$ PRINT/COPIES=4 MYFILE.TXT
If you enter a command longer than one line, you can continue the command onto the next line by following this procedure:
End the command line with a hyphen (-) and press Return.
The system displays an underscore (_) followed by the DCL prompt ($).
Enter the rest of the command line after this prompt.
A line beginning with an underscore means that the system is waiting for your response.
Note the following:
The following example shows how to enter a multiple line command:
$ COPY/LOG FORMAT.TXT,FIGURE.TXT,ARTWORK.TXT - _$ SAVE.TXT
You can use the DCL command PIPE to create complex command processing statements from a single DCL command. For example, you can execute one or more of the following operations from the same DCL command line:
For more detailed information, see Section 16.20 and the description of the PIPE command in the OpenVMS DCL Dictionary: N--Z.
Refer to the OpenVMS Guide to Extended File Specifications for more information about multiple line
commands in an environment employing Extended File Specifications.
3.4 Rules for Entering DCL Commands
The following sections describe specific rules and requirements you must observe when entering a DCL command.
If you are working in an environment with Extended File Specifications, refer to the OpenVMS Guide to Extended File Specifications for rules about using extended file names in DCL commands.
Use any combination of uppercase and lowercase letters. The DCL
interpreter translates lowercase letters to uppercase. Uppercase and
lowercase characters in parameter and qualifier values are equivalent
unless enclosed in quotation marks (" ").
3.4.2 Required Spaces
You cannot specify null characters (<NUL>) on a DCL command line,
even if you enclose the null character in quotation marks.
3.4.5 Maximum Elements
Include no more than 127 elements (parameters, qualifiers, and qualifier values) in each command line.
Each element in a command must not exceed 255 characters. The entire
command must not exceed 1024 characters after all symbols and lexical
functions are converted to their values. You use symbols, described in
Chapter 14, to pass information to the system in an abbreviated
manner. A lexical function, described in Chapter 17, obtains
information from the system, including information about system
processes, batch and print queues, and user processes,
and then substitutes the result of the operation for itself.
3.4.6 Abbreviating Commands
You can abbreviate a command as long as the abbreviated name remains unique among the defined commands on a system. DCL looks only at the first four characters for uniqueness.
The following commands are equal:
$ PRIN/COPI=2 FORMAL_ART.TXT $ PRINT/COPIES=2 FORMAL_ART.TXT
For greater clarity and to ensure that your command procedures are
upwardly compatible, do not abbreviate commands in command procedures.
3.4.7 Additional Rules for Commands in Command Procedures
Additional rules govern the format of commands when they are used in
command procedures. See Chapter 15 and Chapter 16 for more
information about using commands in command procedures.
3.5 Entering Parameters
File specifications are the most common type of parameter. DCL commands can accept input file specifications (files that are acted upon by a command) and output file specifications (files that are created by a command).
The following rules apply when specifying parameters in a command line:
SHOW PRINTER device-name
$ COPY LISTS.TXT FORMAT.TXT
$ COPY PLUTO.TXT,SATURN.TXT,EARTH.TXT PLANETS.TXT
There are three types of qualifiers:
You can abbreviate any qualifier name as long as the abbreviated name remains unique among all qualifier names for the same command. However, to ensure that your command procedures are upwardly compatible, do not abbreviate commands and qualifiers in command procedures.
Commands have default qualifiers; you do not have to specify a
qualifier unless it is different from the command default. The
following sections describe types of qualifiers and qualifier defaults.
The OpenVMS DCL Dictionary contains default information for specific commands.
3.6.1 Command Qualifiers
A command qualifier modifies a command and can appear anywhere in the command line. However, it is a good practice to place the qualifier after the command name. If you are specifying multiple qualifiers, you should place a command qualifier with other command qualifiers that follow the command name.
In the following example, /QUEUE is a command qualifier. The files SATURN.TXT and EARTH.TXT are queued to the print queue LN03_PRINT:
$ PRINT/QUEUE=LN03_PRINT SATURN.TXT,EARTH.TXT
A positional qualifier can modify commands or parameters and has different meanings depending on where you place it in the command string. If you place a positional qualifier after the command but before the first parameter, it affects the entire command string. If you place a positional qualifier after a parameter, it affects only that parameter.
In the following example, the first PRINT command requests two copies of the files SPRING.SUM and FALL.SUM. The second PRINT command requests two copies of the file SPRING.SUM but only one copy of FALL.SUM.
$ PRINT/COPIES=2 SPRING.SUM,FALL.SUM $ PRINT SPRING.SUM/COPIES=2,FALL.SUM
A parameter qualifier can be used only with certain types of parameters, such as input files and output files. For example, the BACKUP command accepts several parameter qualifiers that apply only to input and output file specifications.
In the following example, the /CREATED and /BEFORE qualifiers, which can be specified only with input files, select specific input files for the backup operation. The asterisk (*) is a wildcard character that replaces the file name. BACKUP selects all files with the .TXT file type that were created before December 11, 1999.
$ BACKUP *.TXT/CREATED/BEFORE=11-DEC-1999 NEWFILE.TXT
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