Brian - try this:
# Path to this current makefile
MAKEFILE=$(lastword $(MAKEFILE_LIST))
# constructed path to a subdirectory to hold datestamp files
DATESTAMP=$(MAKEFILE).d/datestamp
# rule to create datestamp files, copying the files date
$(DATESTAMP)/%: %
mkdir -p $(@D) ; \
touch -r $* $@
T: O $(DATESTAMP)/O
cat O > T
~Malcolm
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Brian
> J. Murrell
> Sent: Monday, December 03, 2012 6:00 PM
> To: [email protected]
> Subject: Re: using the date relationship of two older files as a prerequisite
>
> On 12-11-29 12:50 PM, Brian J. Murrell wrote:
> > I have a file which is not created by make but is created/updated by an
> > outside process. The time stamp on this file will always be some time
> > in the past. Let's call this file "O".
> >
> > I have a target which I want make to build which we'll call "T". I want
> > T rebuilt if file O is newer than it was the last time T was built. But
> > even though the time on O might be newer than it was the last time T was
> > built, it will still not be newer than T.
>
> I think I've figured it out:
>
> FORCE:
>
> T: $(shell [[ O -nt O-stamp ]] && echo "FORCE")
> touch T
> touch -r O O-stamp
>
> It seems a shame to have to call out the shell to perform one of the
> functions at the heart of make (comparing the modification time of two
> files) but I couldn't figure out any way to make make do that.
>
> Still open to suggestions. :-)
>
> Cheers,
> b.
>
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