m4: 5 Places You Should Use It

The utility m4 is underutilized and underappreciated, and when paired with make can be indispensible. The mailer sendmail has made m4 legendary, and behind GNU autotools is a lot of serious m4 code. Why not use it for other purposes as well?

Here are some areas in which m4 can be used to ease your work:

• cfengine. You can template the configuration of a “standard file” or a “standard directory” as m4 macros and save yourself a lot of typing (and errors). You could also define a standard “shell script” configuration and use m4 to create it every time.
• Nagios. Nagios configurations benefit a lot from heavy use of m4. Macros can be used to template large configurations, and to template standard configurations.
• DHCP server. A DHCP server can be set up to assign specific addresses to specific hosts; the configuration, however, can be tedious if there are more than a couple of hosts. Macros can be used to simplify static host configurations.
• rpmrc. The /etc/rpmrc file is used to configure RPM during package build time. While not used as heavily, m4 can be used to create an rpmrc file specially tailored for the type of CPU running – this configuration will then be used when RPMs are built.
• HTML generation. When creating hand-crafted HTML, m4 macros can simplify the creation of the standard tags, especially taking care of the beginning and ending tags transparently with only the content visible.

m4 makes templating easy. Anywhere that you need to set up a configuration with multiple sizable elements, m4 can help. A single m4 macro can expand to numerous configuration lines, and a couple dozen m4 lines can result in an extensive configuration set.

Using m4 macros in this manner prevents errors (because of less typing) and all appropriate configuration elements are the same (no mistaken copies).

m4 also adds “include” file capabilities to any configuration file where it is used. This permits common configurations to be reused everywhere, even though the configuration file may not support include files directly.

Even though make is not present on most system installs, m4 is. Adding make will complete this pair and set you on your way to automatic configuration. Try it today!