define Statement--Define a Substitution Variable
Use the define statement to define a substitution variable and, optionally, assigns a value to it. The name of the substitution variable can only contain alphanumeric characters and underscores. You can optionally specify a value, which can be a numeric expression, a character string expression, or a Boolean expression.
Character strings must be in single quotes. Character strings can be concatenated with a plus sign (+). Numeric expressions can include standard operators. An expression can be another substitution variable, in single quotes. The expression evaluates to the value of the quoted substitution variable, because the value assigned to a $variable is substituted everywhere, even inside quoted strings and comments.
If no expression is given for a $variable in the define statement, the $variable is created with no value. The $variable can be used in an ifdef statement.
This statement has the following syntax:
##define $variable [expression | Boolean expression]
Examples--define statement:
## define $tbl 'tf'
## define $i 1
## define $ft '$tbl' + '$i'
String concatenation: this evaluates to tf1 if the first two are defined as shown:
## define $ft '$tbl$i'
Same as above:
## define $i $i+1
## define $i $a+$b+\
$c+$d