Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 101)

Chapter 8: Functions for Transforming Text 91

undeﬁned before the foreach function call, it is undeﬁned after the call. See Section 6.2

[The Two Flavors of Variables], page 60.

You must take care when using complex variable expressions that result in variable

names because many strange things are valid variable names, but are probably not what

you intended. For example,

files := $(foreach Esta-escrito-en-espanol!,b c ch,$(find_files))

might be useful if the value of find_files references the variable whose name is

‘Esta-escrito-en-espanol!’ (es un nombre bastante largo, no?), but it is more likely to

be a mistake.

8.6 The file Function

The file function allows the makeﬁle to write to a ﬁle. Two modes of writing are supported:

overwrite, where the text is written to the beginning of the ﬁle and any existing content is

lost, and append, where the text is written to the end of the ﬁle, preserving the existing

content. In all cases the ﬁle is created if it does not exist.

The syntax of the file function is:

$(file op filename[,text])

The operator op can be either > which indicates overwrite mode, or >> which indicates

append mode. The ﬁlename indicates the ﬁle to be written to. There may optionally be

whitespace between the operator and the ﬁle name.

When the file function is expanded all its arguments are expanded ﬁrst, then the ﬁle

indicated by ﬁlename will be opened in the mode described by op. Finally text will be

written to the ﬁle. If text does not already end in a newline, even if empty, a ﬁnal newline

will be written. If the text argument is not given, nothing will be written. The result of

evaluating the file function is always the empty string.

It is a fatal error if the ﬁle cannot be opened for writing, or if the write operation fails.

For example, the file function can be useful if your build system has a limited command

line size and your recipe runs a command that can accept arguments from a ﬁle as well.

Many commands use the convention that an argument preﬁxed with an @ speciﬁes a ﬁle

containing more arguments. Then you might write your recipe in this way:

program: $(OBJECTS)

$(CMD) $(CMDFLAGS) @[email protected]

If the command required each argument to be on a separate line of the input ﬁle, you

might write your recipe like this:

program: $(OBJECTS)

$(file >[email protected]) $(foreach O,$^,$(file >>[email protected],$O))

$(CMD) $(CMDFLAGS) @[email protected]

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