Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 73)

Chapter 6: How to Use Variables 63

For example:

foo := a.o b.o c.o

bar := $(foo:%.o=%.c)

sets ‘bar’ to ‘a.c b.c c.c’.

6.3.2 Computed Variable Names

Computed variable names are a complicated concept needed only for sophisticated makeﬁle

programming. For most purposes you need not consider them, except to know that making

a variable with a dollar sign in its name might have strange results. However, if you are the

type that wants to understand everything, or you are actually interested in what they do,

read on.

Variables may be referenced inside the name of a variable. This is called a computed

variable name or a nested variable reference. For example,

x = y

y = z

a := $($(x))

deﬁnes a as ‘z’: the ‘$(x)’ inside ‘$($(x))’ expands to ‘y’, so ‘$($(x))’ expands to ‘$(y)’

which in turn expands to ‘z’. Here the name of the variable to reference is not stated

explicitly; it is computed by expansion of ‘$(x)’. The reference ‘$(x)’ here is nested within

the outer variable reference.

The previous example shows two levels of nesting, but any number of levels is possible.

For example, here are three levels:

x = y

y = z

z = u

a := $($($(x)))

Here the innermost ‘$(x)’ expands to ‘y’, so ‘$($(x))’ expands to ‘$(y)’ which in turn

expands to ‘z’; now we have ‘$(z)’, which becomes ‘u’.

References to recursively-expanded variables within a variable name are re-expanded in

the usual fashion. For example:

x = $(y)

y = z

z = Hello

a := $($(x))

deﬁnes a as ‘Hello’: ‘$($(x))’ becomes ‘$($(y))’ which becomes ‘$(z)’ which becomes

‘Hello’.

Nested variable references can also contain modiﬁed references and function invocations

(see Chapter 8 [Functions for Transforming Text], page 83), just like any other reference.

For example, using the subst function (see Section 8.2 [Functions for String Substitution

and Analysis], page 84):

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