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Defined Macros
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31.9 Pitfalls

  • Macros that are given values while sendmail processes mail may not get the value expected. If that happens, careful hand-tracing of rule sets is required to find the fault. For example, the value in $g (see Section 31.10.16, $g ) is the result of sender address rewriting and rewriting by the rule set that is specified in the S= equate of the selected delivery agent. Because $g is used to define the From: header line, errors in that line should be traced through errors in the S= equate's rule set.

  • Macros can have other macros as their values. The sendmail program expands macros recursively. As a consequence, unintentional loops in macro definitions can cause sendmail to appear to hang and to eventually segmentation fault and core dump.

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31.8 Macros with the m4 Technique Book Index 31.10 Alphabetized Reference