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3.4 The Variable `MAKEFILES'                            

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If the environment variable `MAKEFILES' is defined, `make' considers 

its value as a list of names (separated by whitespace) of additional

makefiles to be read before the others.  This works much like the 

`include' directive: various directories are searched for those files  

(*note Including Other Makefiles: Include.).  In addition, the default 

goal is never taken from one of these makefiles (or any makefile 

included by them) and it is not an error if the files listed in  

`MAKEFILES' are not found.                            

                            

   The main use of `MAKEFILES' is in communication between recursive 

invocations of `make' (*note Recursive Use of `make': Recursion.).  It 

usually is not desirable to set the environment variable before a 

top-level invocation of `make', because it is usually better not to 

mess with a makefile from outside.  However, if you are running `make' 

without a specific makefile, a makefile in `MAKEFILES' can do useful  

things to help the built-in implicit rules work better, such as    

defining search paths (*note Directory Search::).                            

                            

   Some users are tempted to set `MAKEFILES' in the environment

automatically on login, and program makefiles to expect this to be done.

This is a very bad idea, because such makefiles will fail to work if 

run by anyone else.  It is much better to write explicit `include' 

directives in the makefiles.  *Note Including Other Makefiles: Include.  

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3.4 变量 MAKEFILES

如果 环境变量 MAKEFILES 被定义了，那么 make 会在读取其他 makefile之前，先读取 MAKEFILES定义的列表中的名字(由空格分隔)。这有点像 include 指令：各目录会被搜索(*note Including Other Makefiles:Include.)。并且，缺省的终点也不会从这些makefile(或被其包含的makefile)中获得,如果找不到相应的 makefile， 也不会报错。

 

'MAKEFILES' 的主要用途是在 递归调用(*note Recursive Use of 'make') make 时进行通信。

通常在顶层调用 make 之前，是不推荐设置 此环境变量的，因为通常***不要和外面的makefile混淆。

但是如果你运行 make 时，没有指定一个特定的 makefile, 那么 MAKEFILES 中定义的 makefile可以做一些有益的事情来帮助使隐式规则运行得更好，例如定义搜索路径(*note Directory Search)

 

有些用户试图在设置在 登录后自动设置 MAKEFILES 环境变量，并且编排 makefile使得此种设定生效。

这是一个坏主意，因为如此一来，它同时被其他人运行时，就会出错退出。更好的办法是在 makefile中写include 指令。 *Note Including Other Makefiles: Include.

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本文转自健哥的数据花园博客园博客，原文链接：http://www.cnblogs.com/gaojian/archive/2012/09/14/2684802.html，如需转载请自行联系原作者