17.2.3.2 HACK( ) m4 macro
Some things just can??™t be called features. To make this clear, they go in the hack
directory and are referenced using the HACK m4 macro. They tend to be sitedependent:
HACK(`cssubdomain??)
This illustrates use of the Berkeley-dependent cssubdomain hack (that makes sendmail
accept local names in either Berkeley.EDU or CS.Berkeley.EDU).
Another way to think of a hack is as a transient feature. Create and use HACK as a
temporary solution to a temporary problem. If a solution becomes permanent, move
it to the FEATURE directory and reference it there.
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594 | Chapter 17: Configure sendmail.cf with m4
17.3 m4 Macros by Function
The m4 technique uses a huge number of macros to accomplish the complex task of
creating configuration files for all possible circumstances. Many are detailed in the
reference section at the end of this chapter. Many others are documented in chapters
dedicated to particular subjects. Here, we summarize many of the m4 macros by
classification or function. Note that a comprehensive list of all m4 macros is available
in Appendix A on page 1227.
17.3.1 Options
Options can be set, unset, and changed in your mc file withsimple define statements.
For example, the following line sets the location of the aliases file and thus
the AliasFile option:
define(`ALIAS_FILE??, `nis:-N mail.
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