Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 66)

56 GNU make

Normally, you do not need to specify this option because ‘make’ does it for you: ‘-w’

is turned on automatically when you use the ‘-C’ option, and in sub-makes. make will

not automatically turn on ‘-w’ if you also use ‘-s’, which says to be silent, or if you use

‘--no-print-directory’ to explicitly disable it.

5.8 Deﬁning Canned Recipes

When the same sequence of commands is useful in making various targets, you can deﬁne

it as a canned sequence with the define directive, and refer to the canned sequence from

the recipes for those targets. The canned sequence is actually a variable, so the name must

not conﬂict with other variable names.

Here is an example of deﬁning a canned recipe:

define run-yacc =

yacc $(firstword $^)

mv y.tab.c $@

endef

Here run-yacc is the name of the variable being deﬁned; endef marks the end of the

deﬁnition; the lines in between are the commands. The define directive does not expand

variable references and function calls in the canned sequence; the ‘$’ characters, parentheses,

variable names, and so on, all become part of the value of the variable you are deﬁning. See

Section 6.8 [Deﬁning Multi-Line Variables], page 69, for a complete explanation of define.

The ﬁrst command in this example runs Yacc on the ﬁrst prerequisite of whichever rule

uses the canned sequence. The output ﬁle from Yacc is always named y.tab.c. The second

command moves the output to the rule’s target ﬁle name.

To use the canned sequence, substitute the variable into the recipe of a rule. You

can substitute it like any other variable (see Section 6.1 [Basics of Variable References],

page 59). Because variables deﬁned by define are recursively expanded variables, all the

variable references you wrote inside the define are expanded now. For example:

foo.c : foo.y

$(run-yacc)

‘foo.y’ will be substituted for the variable ‘$^’ when it occurs in run-yacc’s value, and

‘foo.c’ for ‘$@’.

This is a realistic example, but this particular one is not needed in practice because

make has an implicit rule to ﬁgure out these commands based on the ﬁle names involved

(see Chapter 10 [Using Implicit Rules], page 111).

In recipe execution, each line of a canned sequence is treated just as if the line appeared

on its own in the rule, preceded by a tab. In particular, make invokes a separate sub-shell for

each line. You can use the special preﬁx characters that aﬀect command lines (‘@’, ‘-’, and

‘+’) on each line of a canned sequence. See Chapter 5 [Writing Recipes in Rules], page 41.

For example, using this canned sequence:

define frobnicate =

@echo "frobnicating target $@"

frob-step-1 $< -o $@-step-1

frob-step-2 $@-step-1 -o $@

endef

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