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let me rephrase that -- question about empty commands

From: Robert P. J. Day
Subject: let me rephrase that -- question about empty commands
Date: Mon, 15 Dec 2003 09:19:20 -0500 (GMT-05:00)

  realizing that my previous posting was done without the aid of coffee,
and is not as clear as it could be, let me try again -- sorry for being

  specifically, how does "make" process an empty command; that is,
a command of the form:

     target: ;

  in the context of section 3.8 of the make manual, this kind of target
being used as a prerequisite is apparently being used to *force* the
re-evaluation of another target.  but why does it work that way?

  the fact that it has no commands is obviously used to make sure
that no implicit rules will be used to try to build the target name, that
much is easy.

  but, given that there are no prerequisites, what does this mean in
terms of needing to be processed?  that is, if there are no pre-reqs
in the above rule, what does it mean to say that it's out of date and
has to be "rebuilt" and will therefore force rebuilding on the rule for
which it is a prerequisite?

  and what if (perchance) someone just happens to create a file
called "target" in this directory?  how does that affect the processing?
or does it?

  sorry if all this is obvious, but it's just one of those picky details i'd
like to nail down.


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