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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 ...

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