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22.2 Access Classes in Rules | 863
One possible pitfall is the temptation to define an identical class macro??™s values in
both your domain record and individual host records. If you do, the lookup will be
additive, adding record values from both the domain and the host records.
22.2 Access Classes in Rules
Class macros are useful only in the LHS of rules. The sendmail program offers two
ways to use them:
$=X
The $= prefix causes sendmail to seek a matchbetween the workspace and one of
the words in a class list.*
$~X
The $~ prefix causes sendmail to accept only a single token in the workspace that
does not match any of the words in a class list.
22.2.1 Matching Any in a Class: $=
The list of words that form a class are searched by prefixing the class name with the
characters $=:
R$=X $@<$1>
In this rule, the expression $=X causes sendmail to search a class for the word that is
in the current workspace. If sendmail finds that the word has been defined, and if it
finds that the word is associated with the class $=X, only then is a match made.
The matching word is made available for use in the RHS rewriting. Because the value
of $=X is not known ahead of time, the matched word can be referenced in the RHS
with the $digit positional operator.
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