The right hand side

When the left hand side of a rewriting rule matches, the input is deleted and replaced by the right hand side. Tokens are copied directly from the RHS unless they begin with a dollar sign. Metasymbols are:


$n Substitute indefinite token n from LHS
$[name$] Canonicalize name
$(map key $@arguments $:default $)
Generalized keyed mapping function
$>n "Call" ruleset n
$#mailer Resolve to mailer
$@host Specify host
$:user Specify user

The $ n syntax substitutes the corresponding value from a $+, $-, $*, $=, or $~ match on the LHS. It may be used anywhere.

A host name enclosed between $[ and $] is looked up in the host database(s) and replaced by the canonical name[13]. For example, $[ftp$] might become ftp.CS.Berkeley.EDU and $[[128.32.130.2]$] would become vangogh.CS.Berkeley.EDU. Sendmail recognizes it's numeric IP address without calling the name server and replaces it with it's canonical name.

The $( ... $) syntax is a more general form of lookup; it uses a named map instead of an implicit map. If no lookup is found, the indicated default is inserted; if no default is specified and no lookup matches, the value is left unchanged. The arguments are passed to the map for possible use.

The $> n syntax causes the remainder of the line to be substituted as usual and then passed as the argument to ruleset n. The final value of ruleset n then becomes the substitution for this rule. The $> syntax can only be used at the beginning of the right hand side; it can be only be preceded by $@ or $:.

The $# syntax should only be used in ruleset zero or a subroutine of ruleset zero. It causes evaluation of the ruleset to terminate immediately, and signals to sendmail that the address has completely resolved. The complete syntax is:

$#mailer $@host $:user
This specifies the {mailer, host, user} 3-tuple necessary to direct the mailer. If the mailer is local the host part may be omitted[14]. The mailer must be a single word, but the host and user may be multi-part. If the mailer is the builtin IPC mailer, the host may be a colon-separated list of hosts that are searched in order for the first working address (exactly like MX records). The user is later rewritten by the mailer-specific envelope rewriting set and assigned to the $u macro. As a special case, if the value to $# is local and the first character of the $: value is @, the @ is stripped off, and a flag is set in the address descriptor that causes sendmail to not do ruleset 5 processing.

Normally, a rule that matches is retried, that is, the rule loops until it fails. A RHS may also be preceded by a $@ or a $: to change this behavior. A $@ prefix causes the ruleset to return with the remainder of the RHS as the value. A $: prefix causes the rule to terminate immediately, but the ruleset to continue; this can be used to avoid continued application of a rule. The prefix is stripped before continuing.

The $@ and $: prefixes may precede a $> spec; for example:


R$+ $: $>7 $1
matches anything, passes that to ruleset seven, and continues; the $: is necessary to avoid an infinite loop.

Substitution occurs in the order described, that is, parameters from the LHS are substituted, hostnames are canonicalized, subroutines are called, and finally $#, $@, and $: are processed.

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Last modified: Friday April 02, 1999.