Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 67)

Chapter 5: Writing Recipes in Rules 57

make will not echo the ﬁrst line, the echo command. But it will echo the following two

recipe lines.

On the other hand, preﬁx characters on the recipe line that refers to a canned sequence

apply to every line in the sequence. So the rule:

frob.out: frob.in

@$(frobnicate)

does not echo any recipe lines. (See Section 5.2 [Recipe Echoing], page 43, for a full

explanation of ‘@’.)

5.9 Using Empty Recipes

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:

target: ;

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. The

only reason this is useful is to prevent a target from getting implicit recipes (from implicit

rules or the .DEFAULT special target; see Chapter 10 [Implicit Rules], page 111 and see

Section 10.6 [Deﬁning Last-Resort Default Rules], page 125).

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 Section 4.5 [Phony Targets], page 29, for a better way to do this.

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Roland Ver. 4.5 Informações Técnicas Página 67