GNU make manual 翻译( 一百七十五)

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原文链接：http://www.cnblogs.com/gaojian/archive/2012/10/05/2712160.html

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#操作系统

本文深入探讨了Makefile中`.DEFAULT_GOAL`变量的用途，包括如何设置、查询和重置缺省目标，以及设置多个目标时的注意事项。通过示例展示了`.DEFAULT_GOAL`在不同场景下的应用，帮助开发者更好地理解和利用这一特性。

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.