GNU make manual 翻译( 一百七十五)

`.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.