To illustrate, consider the following rule:
R $+ < @ $+ > $: $>set
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678 | Chapter 18: The R (Rules) Configuration Command
Here, the RHS $>set operator tells sendmail to perform additional rewriting using a
secondary set of rules called set. The workspace is passed as is to that secondary rule set,
and the result of the rewriting by that secondary rule set becomes the new workspace.
The $> operator is described in full in ?§18.7.4 on page 664.
18.9.14 $[ $]
Canonicalize hostname RHS operators
The $[ $] operators are used to convert a non-fully qualified hostname, or a CNAME, into
the official, fully qualified hostname. They are also used to convert square bracket-enclosed
addresses into hostnames. They must be used in a pair with the host or address to be
looked up between them. To illustrate, consider this rule:
R $+ < @ $+ > $: $1 < @ $[ $2 $] >
This rule will match a focused address such as gw<@wash> and cause the host part (the
second $+ on the LHS) to be passed to the RHS (the $2). Because the $2 is between the pair
of $[ $] operators, it is looked up withDNS and converted to a fully qualified hostname.
Thus, the domain dc.gov, for example, will have the host wash fully qualified to become
wash.dc.gov.
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