make depend

[Guy Harris]

> I recently ran across an undocumented flag for cpp that makes the
> following entry for makefiles convenient.  It automagically
> updates file dependencies.  If your cpp doesn't have this
> feature, or you don't like depending on undocumented features,
> you can write you own shell script to accomplish the same thing.
> 
> 	# This has only been tested on 4.2BSD
> 
> 	CPP	=	/lib/cpp
> 	depend	:
> 			{ echo '/^# DO NOT DELETE THIS LINE/+1,$$c';	\
> 			  for i in $(CFILES); do $(CPP) -M $$i; done;	\

Well, I just tested it on 4.2BSD and it says

	0: unknown flag -M

Somebody at your site must have added it to "cpp".  You can do a "cpp -E"
and suck out all the "# <linenumber> <include-file>" lines and make a
list of included files out of that.  "-M" probably just suppresses all
output except lines indicating that an include file is being read.
Unfortunately, if "cpp" isn't a separate program, or if it produces
different kinds of output for included files, or if it doesn't support
"cpp -E", you're out of luck.

	Guy Harris
	{seismo,ihnp4,allegra}!rlgvax!guy