GNU make manual 翻译( 一百七十二)

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6.12 Pattern-specific Variable Values
=====================================

In addition to target-specific variable values (*note Target-specific
Variable Values: Target-specific.), GNU `make' supports
pattern-specific variable values.  In this form, the variable is
defined for any target that matches the pattern specified.

   Set a pattern-specific variable value like this:

     PATTERN ... : VARIABLE-ASSIGNMENT
   where PATTERN is a %-pattern.  As with target-specific variable
values, multiple PATTERN values create a pattern-specific variable
value for each pattern individually.  The VARIABLE-ASSIGNMENT can be
any valid form of assignment.  Any command line variable setting will
take precedence, unless `override' is specified.

   For example:

     %.o : CFLAGS = -O

will assign `CFLAGS' the value of `-O' for all targets matching the
pattern `%.o'.

   If a target matches more than one pattern, the matching
pattern-specific variables with longer stems are interpreted first.
This results in more specific variables taking precedence over the more
generic ones, for example:

     %.o: %.c
             $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@

     lib/%.o: CFLAGS := -fPIC -g
     %.o: CFLAGS := -g

     all: foo.o lib/bar.o

   In this example the first definition of the `CFLAGS' variable will
be used to update `lib/bar.o' even though the second one also applies
to this target. Pattern-specific variables which result in the same
stem length are considered in the order in which they were defined in
the makefile.

   Pattern-specific variables are searched after any target-specific
variables defined explicitly for that target, and before target-specific
variables defined for the parent target.

6.12 模式特定的变量值
=====================================

除了目的特定的变量值(*note Target-specific Variable Values: Target-specific.)，GNU make 还支持模式特定的变量值。此时，变量会为所有匹配的目的定义变量。

设置模式特定的变量看起来像这个样子:

PATTERN ... : VARIABLE-ASSIGNMENT

PATTERN 是一个 %-模式。多模式的值为每一个模式特定的变量单独赋予一个值。VARIABLE-ASSIGNMENT 可以是任何有效的赋值表达式。命令行变量优先级高于这些变量，除非使用了 override。

例如:

%.o : CFLAGS = -O

对任何匹配%.o的目的，将会给 `CFLAGS' 赋值为`-O' 。

如果一个目的匹配了多于一个的模式，拥有更长的枝干的模式特定的变量会首先被翻译。这导致更加特定的变量比更加通用的变量优先级高，例如：

%.o: %.c
$(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@

lib/%.o: CFLAGS := -fPIC -g
%.o: CFLAGS := -g

all: foo.o lib/bar.o

在这个例子中，对 CFLAGS 的第一个定义，将要被运用来更改 lib/bar.o，尽管第二次的定义也满足此目的。拥有同样长度的枝干的模式特定的变量，则按照出现的顺序来确定优先级。

模式特定的变量是在显式定义的目的特定的变量之后，在父目的的目的特定的变量之前被搜索的。

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