It is sometimes useful to define recipes which do nothing. This is done simply by giving a recipe that consists of nothing but whitespace. For example:
defines an empty recipe for
target. You could also use a line
beginning with a recipe prefix character to define an empty recipe,
but this would be confusing because such a line looks empty.
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
special target; see Implicit Rules and see Defining Last-Resort Default Rules).
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
make won’t complain that it
doesn’t know how to build the target, and
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target is out of date.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 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. See Phony Targets, for a better way to do this.