如果未设置变量,则中止makefile

Question

如何根据未设置/值的makefile变量中止make/makefile执行？

我想出了这个,但只有在调用者没有显式运行目标(即make仅运行)时才有效.

ifeq ($(MY_FLAG),)
abort:   ## This MUST be the first target :( ugly
    @echo Variable MY_FLAG not set && false
endif

all:
    @echo MY_FLAG=$(MY_FLAG)

我认为这样的事情是个好主意,但在make的手册中没有找到任何内容:

ifndef MY_FLAG
.ABORT
endif

Answer 1

TL; DR:使用error功能:

ifndef MY_FLAG
$(error MY_FLAG is not set)
endif

请注意,这些行不得缩进.更准确地说,这些行之前不得有任何标签.

通用解决方案

如果您要测试许多变量,那么为此定义一个辅助函数是值得的:

# Check that given variables are set and all have non-empty values,
# die with an error otherwise.
#
# Params:
#   1. Variable name(s) to test.
#   2. (optional) Error message to print.
check_defined = \
    $(strip $(foreach 1,$1, \
        $(call __check_defined,$1,$(strip $(value 2)))))
__check_defined = \
    $(if $(value $1),, \
      $(error Undefined $1$(if $2, ($2))))

以下是如何使用它:

$(call check_defined, MY_FLAG)

$(call check_defined, OUT_DIR, build directory)
$(call check_defined, BIN_DIR, where to put binary artifacts)
$(call check_defined, \
            LIB_INCLUDE_DIR \
            LIB_SOURCE_DIR, \
        library path)

这会输出如下错误:

Makefile:17: *** Undefined OUT_DIR (build directory).  Stop.

笔记:

真正的检查在这里完成:

$(if $(value $1),,$(error ...))

这反映了ifndef条件的行为,因此定义为空值的变量也被视为"未定义".但这仅适用于简单变量和显式空的递归变量:

# ifndef and check_defined consider these UNDEFINED:
explicitly_empty =
simple_empty := $(explicitly_empty)

# ifndef and check_defined consider it OK (defined):
recursive_empty = $(explicitly_empty)

正如@VictorSergienko在评论中所建议的那样,可能需要稍微不同的行为:

$(if $(value $1)测试值是否为非空.如果使用空值定义变量,有时可以.我用了$(if $(filter undefined,$(origin $1)) ...

和:

此外,如果它是一个目录,并且它必须在运行检查时存在,我会使用$(if $(wildcard $1)).但是会是另一个功能.

特定目标检查

也可以扩展解决方案,以便只有在调用某个目标时才需要变量.

$(call check_defined, ...) 从食谱里面

只需将支票移入配方:

foo :
    @:$(call check_defined, BAR, baz value)

前导@符号关闭命令回显并且:是实际命令,shell 无操作存根.

显示目标名称

check_defined可以改进该函数以输出目标名称(通过$@变量提供):

check_defined = \
    $(strip $(foreach 1,$1, \
        $(call __check_defined,$1,$(strip $(value 2)))))
__check_defined = \
    $(if $(value $1),, \
        $(error Undefined $1$(if $2, ($2))$(if $(value @), \
                required by target `$@')))

所以,现在失败的检查会产生一个格式很好的输出:

Makefile:7: *** Undefined BAR (baz value) required by target `foo'.  Stop.

check-defined-MY_FLAG 特殊目标

就个人而言,我会使用上面简单直接的解决方案.但是,例如,此答案建议使用特殊目标来执行实际检查.可以尝试概括并将目标定义为隐式模式规则:

# Check that a variable specified through the stem is defined and has
# a non-empty value, die with an error otherwise.
#
#   %: The name of the variable to test.
#   
check-defined-% : __check_defined_FORCE
    @:$(call check_defined, $*, target-specific)

# Since pattern rules can't be listed as prerequisites of .PHONY,
# we use the old-school and hackish FORCE workaround.
# You could go without this, but otherwise a check can be missed
# in case a file named like `check-defined-...` exists in the root 
# directory, e.g. left by an accidental `make -t` invocation.
.PHONY : __check_defined_FORCE
__check_defined_FORCE :

用法:

foo :|check-defined-BAR

请注意,它check-defined-BAR被列为order-only(|...)先决条件.

优点:

• (可以说)更清晰的语法

缺点:

• 无法指定自定义错误消息
• 运行make -t(请参阅而不是执行配方)将污染具有大量check-defined-...文件的根目录.这是一个令人遗憾的缺点,即无法声明.PHONY模式规则.

我相信,使用一些eval魔术和二次扩展黑客可以克服这些限制,虽然我不确定它是否值得.

Answer 2

使用shell函数test:

foo:
    test $(something)

用法:

$ make foo
test 
Makefile:2: recipe for target 'foo' failed
make: *** [foo] Error 1
$ make foo something=x
test x

Answer 3

另外一个选择：

MY_FLAG = $(error Please set this flag)

尝试在任何地方使用此变量都会导致错误，除非从命令行覆盖它。

要接受环境变量，请使用?=：

MY_FLAG ?= $(error Please set this flag)

Answer 4

您可以使用IF来测试:

check:
        @[ "${var}" ] || ( echo ">> var is not set"; exit 1 )

结果:

$ make check
>> var is not set
Makefile:2: recipe for target 'check' failed
make: *** [check] Error 1

Answer 5

对未设置的变量使用shell错误处理（请注意double $）：

$ cat Makefile
foo:
        echo "something is set to $${something:?}"

$ make foo
echo "something is set to ${something:?}"
/bin/sh: something: parameter null or not set
make: *** [foo] Error 127


$ make foo something=x
echo "something is set to ${something:?}"
something is set to x

如果您需要自定义错误消息，请在后面添加?：

$ cat Makefile
hello:
        echo "hello $${name:?please tell me who you are via \$$name}"

$ make hello
echo "hello ${name:?please tell me who you are via \$name}"
/bin/sh: name: please tell me who you are via $name
make: *** [hello] Error 127

$ make hello name=jesus
echo "hello ${name:?please tell me who you are via \$name}"
hello jesus

Answer 6

为简单起见：

$ cat Makefile
check-%:
        @: $(if $(value $*),,$(error $* is undefined))

bar:| check-foo
        echo "foo is $$foo"

有输出：

$ make bar
Makefile:2: *** foo is undefined. Stop.
$ make bar foo="something"
echo "foo is $$foo"
foo is something