Sendmail, 3rd Edition

The LHS

The LHS of any rule is compared to the current contents of the workspace to determine whether the two match. Table 18-1 displays a variety of special operators offered by sendmail that make comparisons easier and more versatile.

Table 18-1. LHS operators

Operator	§	Description or Use
$*	$*	Match zero or more tokens
$+	$+	Match one or more tokens
$-	$-	Match exactly one token
$@	$@	Match exactly zero tokens (V8 only)
$=	Section 22.2.1	Match any tokens in a class[6]
$~	Section 22.2.2	Match any single token not in a class
$#	$#	Match a literal $#
$|	$|	Match a literal $|
$&	Section 21.5.3	Delay macro expansion until runtime
[6] Class matches either a single token or multiple tokens, depending on the version of sendmail (Section 22.2).

The first three operators in Table 18-1 are wildcard operators, which can be used to match arbitrary sequences of tokens in the workspace. Consider the following rule, which employs the $- operator (match any single token):

R $-     fred.local

Here, a match is found only if the workspace contains a single token (such as tom). If the workspace contains multiple tokens (such as tom@host), the LHS does not match. A match causes the workspace to be rewritten by the RHS to become fred.local. The rewritten workspace is then compared again to the $-, but this time there is no match because the workspace contains three tokens (fred, a dot (.), and local). Because there is no match, the current workspace (fred.local) is carried ...