3.1 Default Preprocessor

The runtime configuration system uses m4 to preprocess the configuration file (see Using Preprocessor to Improve the Configuration.), which makes the configuration extremely flexible. We recommend to use GNU m4 as a preprocessor¹. However, any other implementation of m4 can be used as well. The configure script tries to determine full file name of the preprocessor binary and the necessary command line options. In case it makes a wrong guess, you can instruct it to use a particular preprocessor by using DEFAULT_PREPROCESSOR configuration variable. For example, the following configure invocation instructs it to use /usr/local/bin/gm4:

$ ./configure DEFAULT_PREPROCESSOR="/usr/local/bin/gm4 -s"

Note the use of the -s preprocessor option. It instructs m4 to produce line directives which help dicod produce correct diagnostics about eventual configuration errors. Unless your m4 implementation does not have this feature, we recommend to always use it in DEFAULT_PREPROCESSOR value.

Finally, if you do not wish to use preprocessor at all, you can disable it using --without-preprocessor option to configure.