----僞目標----
target ：
commands
如果makefile 所在目錄沒有target 同名文件：make target 則導致commands 總是被執行。
如果makefile 所在目錄下存在target 同名文件：make target 則commands 不被執行，認爲target 總是最新的。
.PHONY:target
target:
commands
不論makefile 所在目錄下存不存在與target 同名文件，make target 導致commands 的執行，與上一種寫法的區別是引用'.PHONY' 的意義所在。
-----強制目標-----
target:
因爲沒有命令，所以make target ，與makefile 所在目錄下是否存在與target 同名的文件沒有直接關係。
-----雙冒號規則-----
target::
commands
無論makefile 所在目錄下存不存在與target 同名文件，make target 導致commands 的執行，與使用'.PHONY' 定義的僞目標效果相同。
-----------------------------------------------------------------
----------1
.PHONY target
all:target
commands1
# 僞目標
target:
commands
----------2
all:target
commands1
# 僞目標
target:
commands
---------3
all:target
commands1
# 強制目標
target:
---------4
all:target
commands1
# 雙冒號規則
target::
commands
1 和4make all 執行情況相同，無論makefile 所在目錄下存不存在與target 同名文件,commands1 和commands 都被執行。
2 和3make all 執行情況在makefile 所在目錄下存在與target 同名文件，commads 不被執行( 認爲target 目標是最新的) ，commands1 將被執行；而如果不存在與target 同名的文件，則2 運行效果與1 和4 相同，3 運行將導致commands1 的執行。
>rm *
>vim Makefile
>cat -n Makefile
1 .PHONY:target1
2 all1:target1
3 echo "all1_target1_.PHONY_command_all1"
4 target1:
5 echo "all1_target1_.PHONY_command_target1"
6
7 all2:target2
8 echo "all2_target2_command_all2"
9 target2:
10 echo "all2_target2_command_target2"
11
12 all3:target3
13 echo "all3_target3_force_command_all3"
14 target3:
15
16 all4:target4
17 echo "all4_target4_::_command_all4"
18 target4::
19 echo "all4_target4_::_command_target4"
20
>make all1
echo "all1_target1_.PHONY_command_target1"
all1_target1_.PHONY_command_target1
echo "all1_target1_.PHONY_command_all1"
all1_target1_.PHONY_command_all1
>make all2
echo "all2_target2_command_target2"
all2_target2_command_target2
echo "all2_target2_command_all2"
all2_target2_command_all2
>make all3
echo "all3_target3_force_command_all3"
all3_target3_force_command_all3
>make all4
echo "all4_target4_::_command_target4"
all4_target4_::_command_target4
echo "all4_target4_::_command_all4"
all4_target4_::_command_all4
>touch target{1,2,3,4}
>ls
>make all1
echo "all1_target1_.PHONY_command_target1"
all1_target1_.PHONY_command_target1
echo "all1_target1_.PHONY_command_all1"
all1_target1_.PHONY_command_all1
>make all2
echo "all2_target2_command_all2"
all2_target2_command_all2
>make all3
echo "all3_target3_force_command_all3"
all3_target3_force_command_all3
>make all4
echo "all4_target4_::_command_target4"
all4_target4_::_command_target4
echo "all4_target4_::_command_all4"
all4_target4_::_command_all4
-----------
以上測試在GNU Make 3.81 版本進行