linux – Makefile中的$${HOME}或${HOME}？

$cat Makefile 
all:
    echo VAR is ${HOME}
    echo VAR is $${HOME}

给

$make
echo VAR is /home/abc
VAR is /home/abc
echo VAR is ${HOME}
VAR is /home/abc

为什么echo VAR在Makefile中是${HOME}语法工作？我想,要使用shell变量你必须使用$${HOME}}

解决方法:

是的,不是.最好使用$$来明确.但是,there is a special rule for environment variables：

Variables in make can come from the environment in which make is run. Every environment variable that make sees when it starts up is transformed into a make variable with the same name and value. But an explicit assignment in the makefile, or with a command argument, overrides the environment. (If the `-e’ flag is specified, then values from the environment override assignments in the makefile. See section Summary of Options. But this is not recommended practice.)