GNU macro processor
8.2 Searching for include files
GNU m4 allows included files to be found in other directories
than the current working directory.
If a file is not found in the current working directory, and the file
name is not absolute, the file will be looked for in a specified search
path. First, the directories specified with the `-I' option will
be searched, in the order found on the command line. Second, if the
`M4PATH' environment variable is set, it is expected to contain a
colon-separated list of directories, which will be searched in order.
If the automatic search for include-files causes trouble, the `p'
debug flag (see section 6.3 Controlling debugging output) can help isolate the problem.
