Here is the pattern rule to generate a file of prerequisites (i.e.,
a makefile) called `NAME.d' from a C source file called `NAME.c':

     %.d: %.c
             @set -e; rm -f $@; \
              $(CC) -M $(CPPFLAGS) $< > $@.$$$$; \
              sed 's,\($*\)\.o[ :]*,\1.o $@ : ,g' < $@.$$$$ > $@; \
              rm -f $@.$$$$

*Note Pattern Rules::, for information on defining pattern rules.  The
`-e' flag to the shell causes it to exit immediately if the `$(CC)'
command (or any other command) fails (exits with a nonzero status).  

   With the GNU C compiler, you may wish to use the `-MM' flag instead
of `-M'.  This omits prerequisites on system header files.  *Note
Options Controlling the Preprocessor: (gcc.info)Preprocessor Options,
for details.

   The purpose of the `sed' command is to translate (for example):

     main.o : main.c defs.h

into:

     main.o main.d : main.c defs.h

This makes each `.d' file depend on all the source and header files
that the corresponding `.o' file depends on.  `make' then knows it must
regenerate the prerequisites whenever any of the source or header files
changes.