18.9 Rule Operator Reference

In this section we describe each rule operator. Note that we exclude operators that are not germane to rules (such as $?, Section 21.6), and list only those that can be used in rules. Because all rule operators are symbolic, we cannot list them in alphabetical order, so, instead we list them in the alphabetical order of pronunciation. That is, for example, $@ (pronounced dollar-at) comes before $: (pronounced dollar-colon).

To avoid confusion based on different ways of pronouncing symbols, we list all the operators in Table 18-3 so that you can easily find them.

Table 18-3. Operators in rules

Operator	§	RHS or LHS	Description or use
$&	$&	LHS and RHS	Delay macro expansion until runtime
$@	$@	LHS	Match exactly zero tokens (V8 only)
$@	$@	RHS	Rewrite once and return
$@	$@	RHS	Specify host in delivery-agent "triple"
$@	$@	RHS	Specify DSN status in error-agent "triple"
$@	$@	RHS	Specify a database-map argument
$:	$:	RHS	Rewrite once and continue
$:	$:	RHS	Specify address in delivery-agent "triple"
$:	$:	RHS	Specify message in error- or discard-agent "triple"
$:	$:	RHS	Specify a default database-map value
$digit	$digit	RHS	Copy by position
$=	$=	LHS	Match any token in a class
$>	$>	RHS	Rewrite through another rule set (subroutine call)
$[ $]	$[ $]	RHS	Canonicalize hostname
$( $)	$( $)	RHS	Perform a database-map lookup or action
$-	$-	LHS	Match exactly one token
$+	$+	LHS	Match one or more tokens
$#	$#	LHS	Match a literal $#
$#	$#	RHS	Specify a delivery agent
$#	$#	RHS	Specify return for a policy-checking rule set
$*	$*	LHS	Match zero or more tokens
$~	$~	LHS	Match any single token not in a specified class
$|	$|	LHS and RHS	Match or return a literal $|