HP OpenVMS Systems Documentation

Defines a symbolic name for a character string value.

Format

symbol-name :=[=] string

symbol-name[offset,size] :=[=] replacement-string

Parameters

symbol-name

Specifies a string of 1 to 255 characters for the symbol name. The name can contain any alphanumeric characters from the DEC Multinational character set, the underscore (_), and the dollar sign ($). However, the name must begin only with an alphabetic character, an underscore, or a dollar sign. Using one equal sign (:=) places the symbol name in the local symbol table for the current command level. Using two equal signs (:==) places the symbol name in the global symbol table.

string

Names the character string value to be equated to the symbol. The string can contain any alphanumeric or special characters. DCL uses a buffer that is 1024 bytes long to hold a string assignment statement. Therefore, the length of the symbol name, the string, and any symbol substitution within the string cannot exceed 1024 characters.

With the string assignment statement (:=), you do not need to enclose a string literal in quotation marks (" "). String values are converted to uppercase automatically. Also, any leading and trailing spaces and tabs are removed, and multiple spaces and tabs between characters are compressed to a single space.

To prohibit uppercase conversion and to retain required space and tab characters in a string, place quotation marks around the string. To use quotation marks in a string, enclose the entire string within quotation marks and use a double set of quotation marks within the string. For example:

$ TEST := "this is a ""test"" string" $ SHOW SYMBOL TEST TEST = "this is a "test" string"

In this example, the spaces, lowercase letters, and quotation marks are preserved in the symbol definition.

To continue a symbol assignment on more than one line, use the hyphen (-) as a continuation character. For example:

$ LONG_STRING := THIS_SYMBOL_ASSIGNMENT_IS_A_VERY_LONG- _$ _SYMBOL_STRING

To assign a null string to a symbol by using the string assignment statement, do not specify a string. For example:

$ NULL :=

Specify the string as a string literal, or as a symbol or lexical function that evaluates to a string literal. If you use symbols or lexical functions, place single quotation marks (` ') around them to request symbol substitution. See the OpenVMS User's Manual for more information on symbol substitution.

You can also use the string assignment statement to define a foreign command. See the OpenVMS User's Manual for more information about foreign commands.

[offset,size]

Specifies that a portion of a symbol value is to be overlaid with a replacement string. This form of the string assignment statement evaluates the value assigned to a symbol and then replaces the portion of the value (defined by the offset and size) with the replacement string. The brackets are required notation, and no spaces are allowed between the symbol name and the left bracket.

The offset specifies the character position relative to the beginning of the symbol name's string value at which replacement is to begin. Offset values start at 0.

If the offset is greater than the offset of the last character in the string you are modifying, spaces are inserted between the end of the string and the offset where the replacement string is added. The maximum offset value you can specify is 768.

The size specifies the number of characters to replace. Size values start at 1.

Specify the offset and size as integer expressions. See the OpenVMS User's Manual for more information on integer expressions. The value of the size plus the offset must not exceed 769.

replacement-string

Specifies the string that is used to overwrite the string you are modifying. If the replacement string is shorter than the size argument, the replacement string is filled with blanks on the right until it equals the specified size. Then the replacement string overwrites the string assigned to the symbol name. If the replacement string is longer than the size argument, then the replacement string is truncated on the right to the specified size.

You can specify the replacement string as a string literal, or as a symbol or lexical function that evaluates to a string literal. If you use symbols or lexical functions, place single quotation marks (` ') around them to request symbol substitution. For more information on symbol substitution, see the OpenVMS User's Manual.

Examples

$ TIME := SHOW TIME
$ TIME
24-DEC-2001 11:55:44
      

In this example, the symbol TIME is equated to the command string SHOW TIME. Because the symbol name appears as the first word in a command string, the command interpreter automatically substitutes it with its string value and executes the command SHOW TIME.

$ STAT := $DKA1:[TEDESCO]STAT
$ STAT
      

This example shows how to define STAT as a foreign command. The symbol STAT is equated to a string that begins with a dollar sign followed by a file specification. The command interpreter assumes that the file specification is that of an executable image, that is, a file with a file type of .EXE.

When you subsequently enter STAT, the command interpreter executes the image.

$ A = "this is a big     space."
$ SHOW SYMBOL A
  A = "this is a big     space."
$ B := 'A'
$ SHOW SYMBOL B
  B = "THIS IS A BIG SPACE."
      

This example compares the assignment and the string assignment statements. The symbol A is defined using the assignment statement, so lowercase letters and multiple spaces are retained. The symbol B is defined using the string assignment statement. Note that the single quotation marks (` ') are required; otherwise, the symbol name B would have been equated to the literal string A. However, when symbol A's value is assigned to symbol B, the letters are converted to uppercase and multiple spaces are compressed.

$ FILE_NAME := MYFILE
$ FILE_NAME[0,2]:= OL
$ SHOW SYMBOL FILE_NAME
  FILE_NAME = "OLFILE"
      

In this example, the substring expression in the assignment statement overlays the first 2 characters of the string assigned to the symbol FILE_NAME with the letters OL. The offset of 0 requests that the overlay begin with the first character in the string, and the size specification of 2 indicates the number of characters to overlay.

$ FILE_NAME := MYFILE
$ FILE_TYPE := .TST
$ FILE_NAME[F$LENGTH(FILE_NAME),4] := 'FILE_TYPE'
$ SHOW SYMBOL FILE_NAME
  FILE_NAME = "MYFILE.TST"
      

In this example, the symbol name FILE_NAME is equated to the string MYFILE and the symbol name FILE_TYPE is equated to the string .TST. The third assignment statement uses the lexical function F$LENGTH to define the offset value where the overlay is to begin. The symbol name FILE_TYPE is used to refer to the replacement string (.TST). Note that you must use single quotation marks (` ') to request symbol substitution.

The F$LENGTH lexical function returns the length of the string equated to the symbol FILE_NAME; this length is used as the offset. The expression requests that 4 characters of the string currently equated to the symbol FILE_TYPE be placed at the end of the string currently equated to FILE_NAME. The resultant value of the symbol FILE_NAME is MYFILE.TST.