Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 75)

Chapter 6: How to Use Variables 65

ifdef do_sort

func := sort

else

func := strip

endif

bar := a d b g q c

foo := $($(func) $(bar))

attempts to give ‘foo’ the value of the variable ‘sort a d b g q c’ or ‘strip a d b g q c’,

rather than giving ‘a d b g q c’ as the argument to either the sort or the strip function.

This restriction could be removed in the future if that change is shown to be a good idea.

You can also use computed variable names in the left-hand side of a variable assignment,

or in a define directive, as in:

dir = foo

$(dir)_sources := $(wildcard $(dir)/*.c)

define $(dir)_print =

lpr $($(dir)_sources)

endef

This example deﬁnes the variables ‘dir’, ‘foo_sources’, and ‘foo_print’.

Note that nested variable references are quite diﬀerent from recursively expanded vari-

ables (see Section 6.2 [The Two Flavors of Variables], page 60), though both are used

together in complex ways when doing makeﬁle programming.

6.4 How Variables Get Their Values

Variables can get values in several diﬀerent ways:

• You can specify an overriding value when you run make. See Section 9.5 [Overriding

Variables], page 103.

• You can specify a value in the makeﬁle, either with an assignment (see Section 6.5

[Setting Variables], page 65) or with a verbatim deﬁnition (see Section 6.8 [Deﬁning

Multi-Line Variables], page 69).

• Variables in the environment become make variables. See Section 6.10 [Variables from

the Environment], page 70.

• Several automatic variables are given new values for each rule. Each of these has a

single conventional use. See Section 10.5.3 [Automatic Variables], page 120.

• Several variables have constant initial values. See Section 10.3 [Variables Used by

Implicit Rules], page 115.

6.5 Setting Variables

To set a variable from the makeﬁle, write a line starting with the variable name followed

by ‘=’ ‘:=’, or ‘::=’. Whatever follows the ‘=’, ‘:=’, or ‘::=’ on the line becomes the value.

For example,

objects = main.o foo.o bar.o utils.o

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