Introduction to DCL

DCL (Digital Command Language) is an interface between the interactive user and the VAX VMS operating system. When a command is entered by an user, it is executed by the DCL-CLI (Command Language Interpreter) to perform the required actions.

As in case of batch programs in Windows which contains the DOS commands to be executed one after the other; a command procedure in DCL is a collection of DCL commands in the required order of commands to be executed.

When a command is entered in the system, the CLI carries the command. DCL has control over the terminal during an interactive session. A DCL prompt is a '$' sign which states that DCL is ready to accept the next command.

Every DCL command has a basic command format. The first item in a command is a command verb. Command verbs may be entered in their short form as long as the abbreviation is unambiguous. A verb is guaranteed to be unique is four or more letters are specified.

Many commands have one or more parameters following the verb. A parameter filters the action that the verb will perform. There are two types of parameters:

• Required

• Optional

There are eight parameters P1 to P8. Command qualifiers are optional and are separated by slash ("/"). They are used as per the requirements against the command names. The overall format of DCL commands and the rules that govern their format are together called command syntax.

• A command begins with a verb, which may be preceded by one or more spaces. The verb may be abbreviated as long as the abbreviations in unambiguous. Verbs are guaranteed unique if at least four letters are specified.

• A command may take parameters some of which may be compulsory and some may be optional. However, a command may take a maximum of eight parameters. When a parameter contains spaces, commas, slashes it my be enclosed in quotes("").

• Most commands have qualifiers, which consist of a slash ("/") followed by a name. Some qualifiers require a value while for others it is optional. Some qualifiers may have value which are separated from the qualifier with am (=) equal sign. When a qualifier value contains spaces, commas, or slashes it must be enclosed in double quotes ("").

• A command can be continued on additional lines by ending each line with a hyphen (-) except in the last line. The command can be split at any point where a space or a comma appears.

Files and Directories

A file is a collection of data stored in a device. The information of a file is stored in an organized format called records. On VMS, a file is designated by a sequence of characters called a file specification or a file spec. The complete format of the file spec is:

node::device:[directory...]name.type;version