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Chapter 19 V8 m4 Configuration |
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Chapter 19 V8 m4 Configuration |
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The process of building a
sendmail
configuration file begins by creating a file of
m4
statements. Traditionally, the suffix for such files is
.mc
. The
cf/cf
directory contains examples of many
mc
files. Of special interest are those that begin with
generic
, for these can serve as boilerplates in developing your own
mc
files:
generic-bsd4.4.mc generic-solaris2.mc generic-hpux10.mc generic-sunos4.1.mc generic-hpux9.mc generic-ultrix4.mc generic-osf1.mc
All
mc
files require specific minimal statements. For a SunOS 4.1.4 site on the Internet, for example, the following are minimal:
OSTYPE(sunos4.1)dnlsee Section 19.3.1, "OSTYPE()" MAILER(local)dnl
To build a configuration file from these statements, you would place them into a file, say localsun.mc , then run the following command:
%m4 ../m4/cf.m4 localsun.mc > sendmail.cf
Here, the
../m4/cf.m4
tells
m4
where to look for its default configuration file information.
If you are using an old version of m4 , the following error message will be printed:
You need a newer version of M4, at least as new as System V or GNU m4: file not found: NoSuchFile
Just as the messages says, you need a newer version of m4 . (The third line is just a result of forcing m4 to fail and may be safely ignored.) In our localsun.mc example we would need to rerun it as
%/usr/5bin/m4 ../m4/cf.m4 localsun.mc > sendmail.cfSystem V version of m4
Another cause of failure could be that the
../m4/cf.m4
file was not where you thought it was. Various versions of
m4
print this error in different ways:
/usr/5bin/m4:-:1 can't open file
One possible reason for this error might be that you are developing your
mc
file somewhere other than in the
cf/cf
directory. [1] The solution is to use a full pathname to
cf.m4
or to replace that expression on the command line with a shell variable.
[1] This is actually a good idea. It prevents new sendmail distributions from clobbering your
mcfiles.
After you have successfully produced a "first draft" of your configuration file, you can edit localsun.mc and add features as you need them. Many possibilities are described in the rest of this chapter.
It can be advantageous to maintain all the files that make up your local m4 configuration separately from the sendmail distribution. This prevents new releases of sendmail from clobbering your source files. It also allows you to maintain configuration information more conveniently (perhaps under rcs (1) control) and to use programs like make (1) to simplify configuring and installation.
Most modern versions of m4 allow you to define macros on the command line, and one such macro is recognized internally by the m4 technique:
_CF_DIR_
This macro tells m4 where the m4/cf.m4 file described above is located. This macro needs to be set to the cf directory under the sendmail source distribution, and it needs to end in a slash character. For example, GNU m4 version 1.2 allows this:
%setenv CFDIR /usr/local/src/mail/sendmail/cf/%/usr/local/gnu/bin/m4 -D_CF_DIR_=${CFDIR} ${CFDIR}m4/cf.m4 localsun.mc \> sendmail.cf
Notice that we store the value for
_CF_DIR_
in an environmental variable. [2] If your version of
m4
lacks this ability, you should consider upgrading.
[2] Note that gnu m4 can figure out the
_CF_DIR_path itself from the path of the cf.m4 file. We include_CF_DIR_here for example purposes.
By using the _CF_DIR_ macro, configuration and installation can be further simplified by using make (1). To illustrate, consider the following few lines from a Makefile on a SunOS system:
M4=/usr/local/gnu/bin/m4 CFDIR=/usr/local/src/mail/sendmail/cf/ localsun: localsun.mc $(M4) -D_CF_DIR_=$(CFDIR) $(CFDIR)/m4/cf.m4 localsun.mc > sendmail.cf
With this Makefile the above two complex command lines are reduced to a single, simple command line:
%make
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| 19.1 The m4 Preprocessor |
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19.3 The Minimal mc File |