Bash 片段在 makefile 中不起作用

Bash snippet doesn't work in makefile

提问by ART

I have one version file verfilewhich contains below version string
V1.1.2

我有一个verfile包含以下版本字符串的版本文件
V1.1.2

And in Makefile I intend to read this version string, So I wrote Makefile as follows,

而在 Makefile 中我打算读取这个版本字符串，所以我写了 Makefile 如下，

filepath        :=      $(PWD)
versionfile     :=      $(filepath)/verfile

all:
        cat $(versionfile)
        version=$(shell cat $(versionfile))
        echo "version=$(version)"

Now when I run the make file I get following ouput

现在，当我运行 make 文件时，我得到以下输出

cat /home/ubuntu/ankur/verfile
v1.1.2
version=v1.1.2
echo "version="
version=

So I am not able to store version string in the variable and use it later, I am not sure what am I doing wrong?

所以我无法将版本字符串存储在变量中并在以后使用它，我不确定我做错了什么？

Any suggestion/pointer ?

任何建议/指针？

After reading answer from "Didier Trosset" I changed my makefile as follows,

阅读“Didier Trosset”的答案后，我按如下方式更改了我的makefile，

filepath        :=      $(PWD)
versionfile     :=      $(filepath)/verfile
myversion       :=      ""

all:

ifeq ($(wildcard $(versionfile)),)
all:
        echo "File not present"
else
all: myversion = $(shell cat $(versionfile))
endif
all:
        echo "myversion = $(myversion)"

and below is output for the

下面是输出

echo "myversion = v1.1.2"
myversion = v1.1.2

回答by hlovdal

You have two problems. First to have bash (and not make) expand the variable you need to use $$version(or $${version}). By this Make first translates $$into just $and then bash will see $version(or ${version}). Secondly each line in the rule will be executed as a separate command, so in order to let them interact via environmental variables you have to put them into a common subshell, enclosing with paranthesis.

你有两个问题。首先让bash（而不是make）扩展您需要使用的变量$$version（或$${version}）。通过这个 Make 首先转换$$为 just$然后 bash 将看到$version（或${version}）。其次，规则中的每一行都将作为单独的命令执行，因此为了让它们通过环境变量进行交互，您必须将它们放入一个公共子外壳中，并用括号括起来。

filepath        :=      $(PWD)
versionfile     :=      $(filepath)/verfile

all:
    cat $(versionfile)
    (version=$(shell cat $(versionfile)); echo "version=$$version")

回答by Didier Trosset

I usually prefer to have this version string in a makevariable.

我通常更喜欢将这个版本字符串放在一个make变量中。

Therefore, I'd rather use the following that keeps variables into variables, and rules/target/commands in rules/target/commands.

因此，我宁愿使用以下内容将变量保存在变量中，并将规则/目标/命令保存在规则/目标/命令中。

filepath        :=      $(PWD)
versionfile     :=      $(filepath)/verfile
version         :=      $(shell cat $(versionfile))

info:
        echo "version=$(version)"

Note that here, versionis a real make variable. (As opposed to a bash variable existing only in a lingle rule line of the target.)

注意这里，version是一个真正的make变量。（与仅存在于目标的 lingle 规则行中的 bash 变量相反。）

---

---

If you need some commands to create the versionfilethen it'd be better to create this file on its own target

如果你需要一些命令来创建versionfile那么最好在它自己的目标上创建这个文件

filepath        :=      $(PWD)
versionfile     :=      $(filepath)/verfile

all: versionfile
        echo "version=$(version)"

all: version = $(shell cat $(versionfile))

versionfile:
        # Create your version file here

Note that you cannot use the :=anymore for the target variable: it would read the file at Makefile reading instead of when used, i.e. after versionfiletarget has been created.

请注意，您不能:=再对目标变量使用 ：它会在 Makefile 读取时读取文件，而不是在使用时读取文件，即在versionfile创建目标之后。