Name
$[ $]
Synopsis
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 with
DNS 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. These $[ $]
operators can be used only on the RHS, and are fully described in
Section 23.4.3.
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