GNU make manual 翻译( 一百八十七)

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     For example, you might have a list of object files:



          objects = foo.o bar.o baz.o



     To get the list of corresponding source files, you could simply

     write:



          $(objects:.o=.c)



     instead of using the general form:



          $(patsubst %.o,%.c,$(objects))



`$(strip STRING)'

     Removes leading and trailing whitespace from STRING and replaces

     each internal sequence of one or more whitespace characters with a

     single space.  Thus, `$(strip a b  c )' results in `a b c'.



     The function `strip' can be very useful when used in conjunction

     with conditionals.  When comparing something with the empty string

     `' using `ifeq' or `ifneq', you usually want a string of just

     whitespace to match the empty string (*note Conditionals::).



     Thus, the following may fail to have the desired results:



          .PHONY: all

          ifneq   "$(needs_made)" ""

          all: $(needs_made)

          else

          all:;@echo 'Nothing to make!'

          endif



     Replacing the variable reference `$(needs_made)' with the function

     call `$(strip $(needs_made))' in the `ifneq' directive would make

     it more robust.



`$(findstring FIND,IN)'

     Searches IN for an occurrence of FIND.  If it occurs, the value is

     FIND; otherwise, the value is empty.  You can use this function in

     a conditional to test for the presence of a specific substring in

     a given string.  Thus, the two examples,



          $(findstring a,a b c)

          $(findstring a,b c)



     produce the values `a' and `' (the empty string), respectively.

     *Note Testing Flags::, for a practical application of `findstring'.



`$(filter PATTERN...,TEXT)'

     Returns all whitespace-separated words in TEXT that _do_ match any

     of the PATTERN words, removing any words that _do not_ match.  The

     patterns are written using `%', just like the patterns used in the

     `patsubst' function above.



     The `filter' function can be used to separate out different types

     of strings (such as file names) in a variable.  For example:



          sources := foo.c bar.c baz.s ugh.h

          foo: $(sources)

                  cc $(filter %.c %.s,$(sources)) -o foo



     says that `foo' depends of `foo.c', `bar.c', `baz.s' and `ugh.h'

     but only `foo.c', `bar.c' and `baz.s' should be specified in the

     command to the compiler.

例如，你可以有一个目标文件的列表：

objects = foo.o bar.o baz.o

为了得到相应的源文件的列表，你可以简单地写：

$(objects:.o=.c)

而不是使用:

$(patsubst %.o,%.c,$(objects))

`$(strip STRING)'

从STRING 里面去除前面的和后面的空格，并且将内在的一个或多个空格序列替换为一个单独的空格。因此，$(strip a b c) 的结果是 a b c。

strip 函数当何条件式结合的时候，可以非常游泳。当和空字符串比较时用 ifeq 或者 ifneq，你通常想要几个只有空格的字符串来匹配空字符串(*note Conditionals::)。

因此，下列的可能会无法达成想要的结果:

.PHONY: all
ifneq "$(needs_made)" ""
all: $(needs_made)
else
all:;@echo 'Nothing to make!'
endif

在ifneq 指令中把变量参照 $(needs_made)替为函数调用 $(strip $(needs_made))可能会更加的健壮。

以下一段，因故暂停。

`$(findstring FIND,IN)'
Searches IN for an occurrence of FIND. If it occurs, the value is
FIND; otherwise, the value is empty. You can use this function in
a conditional to test for the presence of a specific substring in
a given string. Thus, the two examples,

$(findstring a,a b c)
$(findstring a,b c)

produce the values `a' and `' (the empty string), respectively.
*Note Testing Flags::, for a practical application of `findstring'.

`$(filter PATTERN...,TEXT)'
Returns all whitespace-separated words in TEXT that _do_ match any
of the PATTERN words, removing any words that _do not_ match. The
patterns are written using `%', just like the patterns used in the
`patsubst' function above.

The `filter' function can be used to separate out different types
of strings (such as file names) in a variable. For example:

sources := foo.c bar.c baz.s ugh.h
foo: $(sources)
cc $(filter %.c %.s,$(sources)) -o foo

says that `foo' depends of `foo.c', `bar.c', `baz.s' and `ugh.h'
but only `foo.c', `bar.c' and `baz.s' should be specified in the
command to the compiler.

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