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* doc/make.texi: [SV 35455] Add more uses for Empty Recipes.

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Paul Smith 2016-02-28 12:35:15 -05:00
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@ -4970,27 +4970,24 @@ beginning with a recipe prefix character to define an empty recipe,
but this would be confusing because such a line looks empty.
@findex .DEFAULT@r{, and empty recipes}
You may be wondering why you would want to define a recipe that
does nothing. The only reason this is useful is to prevent a target
from getting implicit recipes (from implicit rules or the
@code{.DEFAULT} special target; @pxref{Implicit Rules} and
@pxref{Last Resort, ,Defining Last-Resort Default Rules}).@refill
You may be wondering why you would want to define a recipe that does
nothing. One reason this is useful is to prevent a target from
getting implicit recipes (from implicit rules or the @code{.DEFAULT}
special target; @pxref{Implicit Rules} and @pxref{Last Resort,
,Defining Last-Resort Default Rules}).@refill
@c !!! another reason is for canonical stamp files:
@ignore
@example
foo: stamp-foo ;
stamp-foo: foo.in
create foo frm foo.in
touch $@
@end example
@end ignore
Empty recipes can also be used to avoid errors for targets that will
be created as a side-effect of another recipe: if the target does not
exist the empty recipe ensures that @code{make} won't complain that it
doesn't know how to build the target, and @code{make} will assume the
target is out of date.
You may be inclined to define empty recipes for targets that are
not actual files, but only exist so that their prerequisites can be
You may be inclined to define empty recipes for targets that are not
actual files, but only exist so that their prerequisites can be
remade. However, this is not the best way to do that, because the
prerequisites may not be remade properly if the target file actually does exist.
@xref{Phony Targets, ,Phony Targets}, for a better way to do this.
prerequisites may not be remade properly if the target file actually
does exist. @xref{Phony Targets, ,Phony Targets}, for a better way to
do this.
@node Using Variables, Conditionals, Recipes, Top
@chapter How to Use Variables