sendmail, 4th Edition

The LHS

The LHS of any rule is compared to the current contents of the workspace to determine whether the two match. Table 18-2 displays a variety of special operators offered by sendmail that make comparisons easier and more versatile.

Table 18-2. LHS operators

Operator	§	Description or use
[a]
$*	$* on page 681	Match zero or more tokens.
$+	$+ on page 679	Match one or more tokens.
$-	$- on page 679	Match exactly one token.
$@	$@ on page 673	Match exactly zero tokens (V8 only).
$=	Matching Any in a Class: $= on page 863	Match any tokens in a class.[a]
$˜	Matching Any Token Not in a Class: $~ on page 864	Match any single token not in a class.
$#	$# on page 680	Match a literal $#.
$|	$| on page 682	Match a literal $|.
$&	Use Value As Is with $& on page 793	Delay macro expansion until runtime.
[a] a Class matches either a single token or multiple tokens, depending on the version of sendmail (Access Classes in Rules).

The first three operators in Table 18-2 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 ...