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.
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 |
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 ... |
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