[Chapter 16] 16.2 The null.mc File

16.2 The null.mc File

Now we will create a file called null.mc , which, when later processed, will create a client.cf -style configuration file. The null.mc fill will be very small, containing only these three lines:

include(`../m4/cf.m4')
OSTYPE(`sunos4.1')
FEATURE(`nullclient',`mail.us.edu')

These three lines do everything that the preceding 11 chapters did and more. We discuss them individually, then show how to process the file.

16.2.1 include

Naturally, a configuration is not simply plucked from thin air. Instead the master prototype configuration needs to be read and processed with the following command: [1]

[1] See ../README for a description of how to replace this line with similar information on the command line when processing. The include line inside your null.mc file is portable to all versions of m4 . The command line form is highly version dependent, but allows you to maintain your .mc files outside the sendmail distribution.

include(`../m4/cf.m4')

Note that the expression inside the parentheses begins with a reverse apostrophe and ends with a forward one. These opposing half quotes are used by m4 (1) to prevent a test from being interpreted as a macro. The expression ../m4/cf.m4 is taken to be the pathname of a file. That file is read at this point as though it were actually typed in here.

16.2.2 OSTYPE

A number of values in the configuration file will differ from operating system to operating system. The location of the queue directory, for example, is /var/spool/mqueue for IRIX 5.x but /usr/spool/mqueue for BSD 4.3 Unix. To declare the proper value for your operating system, look in the ../ostype directory:

% 

ls ../ostype


aix3.m4        bsdi1.0.m4     hpux10.m4    linux.m4      sco3.2.m4     ultrix4.m4
amdahl-uts.m4  bsdi2.0.m4     hpux9.m4     nextstep.m4   solaris2.m4   unknown.m4
aux.m4         dgux.m4        irix4.m4     osf1.m4       sunos3.5.m4
bsd4.3.m4      domainos.m4    irix5.m4     ptx2.m4       sunos4.1.m4
bsd4.4.m4      dynix3.2.m4    isc4.1.m4    riscos4.5.m4  svr4.m4

Pick the operating system closest to yours. For SunOS 4.1.4 systems, for example, choose sunos4.1.m4 .

Whichever you choose, include support for it by stripping the .m4 suffix and including the resulting name in an OSTYPE declaration:

        sunos4.1.m4
           


         
becomes

           


OSTYPE(`sunos4.1')

Remember to surround the result in a reverse and forward apostrophe pair.

16.2.3 FEATURE

The last line in our null.mc file provides the magic incantation of a client.cf -style file:

FEATURE(`nullclient',`mail.us.edu')

Two arguments inside the parentheses, separated by a comma, are required. The first argument, nullclient , tells m4 (1) to create a null (do-nothing) client (.cf) file. The second argument is the canonical name of the mail hub. Just as we did for the client.cf file, we use the hostname mail.us.edu . You should, of course, use the canonical name of your own mail hub.