Using include Makefiles

One method of simplifying makefiles, while providing a consistent compilation environment, is to use the make:

	include filename 

This directive reads in the contents of a named makefile; if the named file is not present, make checks for a file by that name in /etc/default.

For instance, there is no need to duplicate the pattern-matching rule for processing troff sources in each makefile, when you can include its target entry, as shown below.

SOURCES= doc.ms spec.ms 
...
clean: $(SOURCES) 
include ../pm.rules.mk

Here, make reads in the contents of the ../pm.rules.mk file:

# pm.rules.mk 
# 
# Simple "include" makefile for pattern-matching 
# rules.  

%.tr: %.ms 
         	troff -t -ms $< > $@ 
%.nr: %.ms 
         	nroff -ms $< > $@