GNU make manual 翻译( 一百七十五)

继续翻译

`.DEFAULT_GOAL'
     Sets the default goal to be used if no targets were specified on
     the command line (*note Arguments to Specify the Goals: Goals.).
     The `.DEFAULT_GOAL' variable allows you to discover the current
     default goal, restart the default goal selection algorithm by
     clearing its value, or to explicitly set the default goal.  The
     following example illustrates these cases:

          # Query the default goal.
          ifeq ($(.DEFAULT_GOAL),)
            $(warning no default goal is set)
          endif

          .PHONY: foo
          foo: ; @echo $@

          $(warning default goal is $(.DEFAULT_GOAL))

          # Reset the default goal.
          .DEFAULT_GOAL :=

          .PHONY: bar
          bar: ; @echo $@

          $(warning default goal is $(.DEFAULT_GOAL))

          # Set our own.
          .DEFAULT_GOAL := foo

     This makefile prints:

          no default goal is set
          default goal is foo
          default goal is bar
          foo

     Note that assigning more than one target name to `.DEFAULT_GOAL' is
     illegal and will result in an error.

`.DEFAULT_GOAL'

设置如果在命令行中没有制定目的场合，缺省的终点(*note Arguments to Specify the Goals :Goals)。

.DEFAULT_GOAL 变量允许你发现当前的缺省的终点，通过清除它的值来重新设置缺省的终点。下面的例子给出了如何操作：

# Query the default goal.
ifeq ($(.DEFAULT_GOAL),)
　　$(warning no default goal is set)
endif

.PHONY: foo
foo: ; @echo $@

$(warning default goal is $(.DEFAULT_GOAL))

# Reset the default goal.
.DEFAULT_GOAL :=

.PHONY: bar
bar: ; @echo $@

$(warning default goal is $(.DEFAULT_GOAL))

# Set our own.
.DEFAULT_GOAL := foo

这个 makefile 输出:

no default goal is set
default goal is foo
default goal is bar
foo

请注意设置多余一个的目的名给`.DEFAULT_GOAL' 是无效的，会造成错误。

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