命令行中的 Makefile 变量与环境中的变量
有没有办法检测变量是否已从环境与命令行中设置？
我想区分使用 make LIB=mylib 调用 make 的人和使用 make 调用 make 并定义 $LIB 的人。
Is there a way to detect whether a variable has been set from the environment vs. on the command line?
I would like to distinguish between someone invoking make with make LIB=mylib vs. make and $LIB being defined.
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是的。您可以使用 origin 函数来确定变量的位置被定义。
ifneq (,$(findstring environment,$(origin LIB))) # LIB was defined by the environment else # LIB was defined some other way endifYes. You can use the origin function to determine where a variable was defined.
ifneq (,$(findstring environment,$(origin LIB))) # LIB was defined by the environment else # LIB was defined some other way endif使用非 Gnu make，您可以针对相关变量运行
export命令和grep。这仅在规则中有效，并且仅在变量未设置为一次性时有效（例如在LIB=foo make中）。With non-Gnu make, you could run the
exportcommand andgrepfor the variable in question. This works only in rules and only as long as the variable is not set as a one-shot (like inLIB=foo make).