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Previous: 38.6 Process-Specified AddressesChapter 38
Rule-Set Testing with -bt
Next: 38.8 Batch Rule-Set Testing

38.7 Add Debugging for Detail

In rule-testing mode the -d rule-testing command can be used to turn debugging output on and off. Prior to V8.7 sendmail the -d could be specified only on the command line. Beginning with V8.7 sendmail, the -d may also be specified in rule-testing mode. We illustrate the latter technique here.

Debugging output can reveal in great detail how individual rules are being handled. A debugging category and level of 21.12, for example, causes sendmail to print the LHS of each rule as it is tried. To illustrate, consider the following (highly simplified) configuration-file rule set:

R@                  $#local $:$n                 handle <> form
R$*<@$+>$*          $#$M $@$R $:$1<@$2>$3        user@some.where
R$+                 $#local $:$1                 local names

Normal output that is produced when a rule-set number and address are entered at the > prompt looks like this:

> 0 george
rewrite: ruleset   0   input: george
rewrite: ruleset   0 returns: $# local $: george

But if we turn on debugging using the -d rule-testing command:

> -d21.12

the output that is produced when the same rule-set number and address are entered is more verbose than it was before:

>  0 george
rewrite: ruleset   0   input: george
---trying rule: @
--- rule fails
---trying rule: $* < @ $+ > $*
--- rule fails
---trying rule: $+
---rule matches: $# local $: $1
rewritten as: $# local $: george
rewrite: ruleset   0 returns: $# local $: george

Observe that the first rule in rule set 0 (the lone @) does not match george in the workspace. Therefore that rule fails and is skipped. Then the more complicated rule ($*<@$+>$*) is tried, and it too fails. Finally, the $+ operator in the last rule matches george, and the workspace is rewritten.

Note that the extra output that is produced by -d can potentially run to many lines. To capture the output for later examination, consider running sendmail in rule-testing mode from within a script(1), emacs(1), or similar session.

Higher levels of debugging are also available for examining rules and rule sets. The level -d21.15 shows $digit operators on the RHS being substituted with values from the LHS. The level -d21.35 causes each comparison, token versus token, to be printed.

To turn off the extra debugging output, just reuse the -d rule-testing command and specify a level of zero:

> -d21.0

A -d with no category or level behaves the same as the -d command-line switch (see Section 37.1, "The Syntax of -d"). It sets a default of 0-99.1.

38.7.1 A Trick

In debugging large configuration files, the output that is produced by the -d21.15 switch can become too huge to examine conveniently. A good alternative (when modifying or adding rules) is to temporarily insert a fake subroutine call before and after individual rules to see what they do:

R$*      $:$>TEST $1       <- fake subroutine call
Rlhs     rhs               <- new rule
R$*      $:$>TEST $1       <- fake subroutine call

With the fake wrapper around the new rule (the name TEST is arbitrary), ordinary rule testing with -bt now shows how the address is rewritten by that rule:

rewrite: ruleset  3   input: ...
rewrite: ruleset TEST   input: ...
rewrite: ruleset TEST returns: ...
                                  <- new rule acted here
rewrite: ruleset TEST   input: ...
rewrite: ruleset TEST returns: ...
rewrite: ruleset  3 returns: ...

If you use this technique, remember, of course, to remove the fake subroutine calls before putting that configuration file into use.

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