10.2.1 The LHS

The wildcard operator in this LHS, the $* , is different from the $+ wildcard operator that you saw in rule set 0. Recall that the $+ wildcard operator matches one or more tokens in the workspace. To review, consider the LHS rule:

$+ @ $+

This LHS easily matches an address like [email protected] in the workspace:

workspace                     LHS
 you               $+       
 match one or more              
 @                 @        
 match exactly              
 here              $+       
 match one              
 .                          
     or more
 us . edu

This same LHS, however, does not match an address like @here.us.edu :

workspace                  LHS
 @               $+       
 match one              
 here                     
     or more              
 . us . edu                              @        
 match exactly, fails!
                 $+

Because the $+ wildcard operator needs to match one or more tokens, it fails when there is nothing in front of the @ .

The $* wildcard operator is just like the $+ wildcard operator, except that it will match nothing (zero tokens). If the LHS had used $* instead of $+ , an address like @here.us.edu would be matched:

workspace                   LHS
                  $*       
 match zero or more (matches zero)              
 @                @        
 match exactly              
 here             $*       
 match zero              
 .                         
     or more
 us . edu

The LHS in rule set 3 matches anything or nothing, provided that there is a pair of angle brackets in the workspace somewhere:

R$* < $* > $*   $2             basic RFC822 parsing

For example, consider an address that might be given to sendmail by your MUA:

Your Fullname <[email protected]>

This address is tokenized and placed into the workspace. That workspace is then compared to the LHS:

workspace                   LHS
 Your             $*       
 match zero              
 Fullname                  
     or more              
 <                <        
 match exactly              
 you              $*       
 match zero              
 @                         
     or more
 here . us . edu >                >        
 match exactly
                  $*       
 match zero or more

10.2.2 The RHS

Recall that the objective of rule set 3 is to strip everything but the address part (the text between the angle brackets). That stripping is accomplished by rewriting the workspace using the $2 positional operator in the RHS:

R$* < $* > $*   $2             basic RFC822 parsing                 

                 
strip all but the address

Remember, when a $ digit appears in the RHS, that digit is used as a count into the wildcard operators of the LHS.

$* < $* > $*          
$1   $2   $3

$1 refers to the first $* , $2 refers to the second, and $3 to the third. Comparing this ordering of operators to the test address, you see

workspace            LHS                                                RHS
 Your         $*    
 match zero
          $1        Fullname           
      or more              
 <            <     
 match exactly              
 you          $*    
 match zero
          $2          @                  
      or more
 here . us . edu >            >     
 match exactly
              $*    
 match zero or more   $3

This illustrates that the middle (second) $* matches the [email protected] part of the workspace. When the RHS rewrites the workspace, it does so by copying the tokens matched by the second wildcard operator (specified in the RHS with the $2 positional operator).

10.2.3 Test Rule Set 3

Take a few moments to experiment. Observe the transformation of a user-specified address into one that sendmail can use. Add the following new rule set 3 to the rule sets in the client.cf file:

S3 # preprocessing for all rule sets                                  


 new
 

R$* < $* > $*       $2                      basic RFC822 parsing      


 new

Now run sendmail again. Up to now, you have been testing rule set 0, so you have specified a 0 following the > prompt. Instead, you will now specify a 3 because you are testing rule set 3:

% 

./sendmail -Cclient.cf -bt

 ADDRESS TEST MODE (ruleset 3 NOT automatically invoked) Enter <ruleset> <address> > 

3 Your Fullname <you@here>

 rewrite: ruleset  3   input: Your Fullname < you @ here > rewrite: ruleset  3 returns: you @ here

As expected, the new rule causes everything except the "good" email address, the address between the angle brackets, to be thrown away.

Before we improve rule set 3, take a few moments to experiment. Experiment by putting the fullname last. Try omitting the email address between the angle brackets. Try nesting angle brackets in an address, like <a<b>c> .

As a closing note, recall that sendmail does the minimum matching possible when comparing operators to the workspace. Although $* , for example, can match zero or more, it prefers to match zero if possible and, if not, to match the fewest tokens possible. A LHS of $*@$+ , for example, will match as shown in Table 10.1 .

Table 10.1: What $* in $*@$+ Matches for Different Addresses

Address	$* matches	@	$+
[email protected]	a.b.c	@	d.e
a@b@c	a	@	b@c
@b@c		@	b@c

Expecting operators to match more than they do can cause you to misunderstand the effect of rules.