sendmail, 4th Edition

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 match between the workspace and one of the words in a class list.^[334]

$˜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.

^{[334] *} With V8 and later, words in a class can be multitokened.