Assignments and Symbols

A variable is an object whose value can change during the running of a REXX program. The process of changing the value of a variable is called assigning a new value to it.

The value of a variable is a single character string, of any length, that can contain any characters.

You can assign a new value to a variable with the ARG, PARSE, or PULL instructions, the VALUE built-in function, or the variable pool interface. The most common way of changing the value of a variable is the assignment instruction itself. Any clause of the following form is taken to be an assignment:

symbol=expression;

The result of expression becomes the new value of the variable named by the symbol to the left of the equal sign. Currently, on VM if you omit expression, the variable is set to the null string. However, it is advisable to set a variable explicitly to the null string: symbol=''. For example:

/* Next line gives FRED the value "Frederic" */
Fred='Frederic'

The symbol that names the variable cannot begin with a digit (0-9) or a period. (Without this restriction on the first character of a variable name, you could redefine a number; for example 3=4; would give a variable called 3 the value 4.)

You can use a symbol in an expression even if you have not assigned it a value, because a symbol has a defined value at all times. A variable you have not assigned a value is uninitialized. Its value is the characters of the symbol itself, translated to uppercase (that is, lowercase a-z to uppercase A-Z). However, if it is a compound symbol, its value is the derived name of the symbol (see Compound symbols). For example:

/* If Freda has not yet been assigned a value,   */
/* then next line gives FRED the value "FREDA"   */
Fred=Freda

The meaning of a symbol in REXX varies according to its context. As a term in an expression (rather than a keyword), a symbol belongs to one of four groups: constant symbols, simple symbols, compound symbols, and stems. Constant symbols cannot be assigned new values. You can use simple symbols for variables where the name corresponds to a single value. You can use compound symbols and stems for more complex collections of variables, such as arrays and lists.