是否可以在Makefile中创建多行字符串变量 [英] Is it possible to create a multi-line string variable in a Makefile

问题描述

我想创建一个makefile变量，该变量是多行字符串(例如，电子邮件发布公告的正文).像

I want to create a makefile variable that is a multi-line string (e.g. the body of an email release announcement). something like

ANNOUNCE_BODY="
Version $(VERSION) of $(PACKAGE_NAME) has been released

It can be downloaded from $(DOWNLOAD_URL)

etc, etc"

但是我似乎找不到解决此问题的方法.有可能吗?

But I can't seem to find a way to do this. Is it possible?

推荐答案

是的，您可以使用define关键字声明多行变量，如下所示:

Yes, you can use the define keyword to declare a multi-line variable, like this:

define ANNOUNCE_BODY
Version $(VERSION) of $(PACKAGE_NAME) has been released.

It can be downloaded from $(DOWNLOAD_URL).

etc, etc.
endef

棘手的部分是将多行变量从Makefile中撤回.如果您只是使用"echo $(ANNOUNCE_BODY)"做显而易见的事情，那么您会看到其他人在此处发布的结果-shell尝试将变量的第二行和后续行作为命令本身处理.

The tricky part is getting your multi-line variable back out of the makefile. If you just do the obvious thing of using "echo $(ANNOUNCE_BODY)", you'll see the result that others have posted here -- the shell tries to handle the second and subsequent lines of the variable as commands themselves.

但是，您可以按原样将变量值作为环境变量导出到Shell，然后从Shell作为环境变量引用它(而不是make变量).例如:

However, you can export the variable value as-is to the shell as an environment variable, and then reference it from the shell as an environment variable (NOT a make variable). For example:

export ANNOUNCE_BODY
all:
    @echo "$$ANNOUNCE_BODY"

请注意使用$$ANNOUNCE_BODY表示外壳环境变量引用，而不是$(ANNOUNCE_BODY)，这将是常规的make变量引用.另外，请确保在变量引用周围使用引号，以确保换行符不会被外壳程序本身解释.

Note the use of $$ANNOUNCE_BODY, indicating a shell environment variable reference, rather than $(ANNOUNCE_BODY), which would be a regular make variable reference. Also be sure to use quotes around your variable reference, to make sure that the newlines aren't interpreted by the shell itself.

当然，此技巧可能对平台和外壳敏感.我在Ubuntu Linux上使用GNU bash 3.2.13对其进行了测试； YMMV.

Of course, this particular trick may be platform and shell sensitive. I tested it on Ubuntu Linux with GNU bash 3.2.13; YMMV.

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