HELP = — VMS 4.6
Defines a symbolic name for a character string or integer value.
Format:
symbol-name =[=] expression
symbol-name[bit-position,size] =[=] replacement-expression
Additional information available:
Parameters
symbol-name Defines a 1- through 255-character alphanumeric string name for the symbol. The symbol name must begin with an alphabetic character (uppercase and lowercase characters are equivalent), an underscore, or a dollar sign. After the first character, the name can contain any alphanumeric characters from the DEC Multinational Character Set, underscores, or dollar signs. If you specify a single equal sign (=) in the assignment statement, the symbol name is placed in the local symbol table for the current command level. If you specify double equal signs (==) in the assignment statement, the symbol name is placed in the global symbol table. expression Specifies the value on the right-hand side of an assignment statement. An expression can consist of a character string value, an integer value, a symbol name, a lexical function, or a combination of these entities. The components of an expression are evaluated, and the result is assigned to a symbol. All literal character strings must be enclosed in quotation marks. If you specify an expression containing a symbol, the command interpreter uses the symbol's value in evaluating the expression. The result of expression evaluation is either a character string or an integer value. The data type of a symbol is determined by the data type of the expression. If the expression evaluates to a string, the symbol is assigned a string value. If the expression evaluates to an integer, the symbol is assigned an integer value. For a summary of operators used in expressions, details on how to specify expressions, and details on how expressions are evaluated, see Chapter 5 of the VAX/VMS DCL Concepts Manual. DCL uses a buffer that is 1024 bytes long to hold an assignment statement, and to evaluate the expression. The length of the symbol name, the expression, and the expression's calculations cannot exceed 1024 bytes. [bit-position,size] Specifies that a binary overlay is to be inserted in the current 32-bit value of a symbol-name. This type of assignment statement evaluates the current value of the symbol-name and replaces the specified number of bits with the result of the replacement-expression. The bit-position is the location relative to bit 0 at which the overlay is to occur. If the symbol that you are overlaying is an integer, then the bit position must be less than 32. Also, the sum of the bit position and the size must be less than or equal to 32. If the symbol you are overlaying is a string, then the bit position must be less than 6152. Because each character is represented using 8 bits, you can begin an overlay at any character through the 768th. (The 768th character starts in bit position 6144.) The sum of the bit position and the size must be less than or equal to 6152. The size is the number of bits to be overlaid. If you specify a size that is greater than 32, then DCL reduces the size to 32. The square brackets are required notation; no spaces are allowed between the symbol name and the left bracket. Specify values for bit-position and size as integer expressions. replacement-expression Specifies the value that is used to overlay the symbol you are modifying. Specify the replacement-expression as an integer expression. If the symbol you are modifying is an integer, the replacement-expression defines a bit pattern which is overlaid on the value assigned to the symbol. If the symbol you are modifying is a character string, the result of the replacement-expression defines a bit pattern which is overlaid on the specified bits of the character string. If the symbol you are modifying is undefined, the result of the replacement-expression is overlaid on a null string.
Examples
1. $ LIST == "DIRECTORY"
$ TIME == "SHOW TIME"
$ QP == "SHOW QUEUE/DEVICE"
$ SS == "SHOW SYMBOL"
The file SYNONYM.COM contains the assignment statements shown; these
are user-defined synonyms for commands. Execute this command
procedure as follows:
$ @SYNONYM
After the command procedure creates the global symbol definitions,
you can use these synonyms (LIST, TIME, QP, and SS) at the
interactive command level. Note that the assignments are global;
otherwise, the symbol names would have been deleted after the file
SYNONYM.COM completed execution.
2. $ COUNT = 0
$ LOOP:
$ COUNT = COUNT + 1
.
.
.
$ IF COUNT .LT.5 THEN GOTO LOOP
The symbol COUNT is initially assigned a numeric value of 0; a loop
is established to increment the value of COUNT by 1 each time the
loop is entered. Note that when the symbol name COUNT appears on
the right-hand side of an arithmetic assignment statement, the
command interpreter automatically substitutes its current value.
The IF command tests the value of COUNT; if it is less than 5, the
procedure branches to the label LOOP and the statements between the
label LOOP through the IF command are executed again. When the
value of the symbol count reaches 5, the loop is not executed again
and the command following the IF command is executed.
3. $ A = 25
$ CODE = 4 + F$INTEGER("6") - A
$ SHOW SYMBOL CODE
CODE = -15 HEX = FFFFFFF1 Octal = 1777761
This example contains two assignment statements. The first
statement assigns the value 25 to the symbol A. The second
assignment statement evaluates an expression containing an integer
(4), a lexical function (F$INTEGER("6")), and the symbol A. The
result of the expression, -15, is assigned to the symbol CODE.