在makefile中，如何获取从一个绝对路径到另一个绝对路径的相对路径？

Question

一个例子来说明我的问题：

顶级makefile

rootdir = $(realpath .)
export includedir = $(rootdir)/include
default:
    @$(MAKE) --directory=$(rootdir)/src/libs/libfoo

src/libfoo 的 Makefile

currentdir = $(realpath .)
includedir = $(function or magic to make a relative path
               from $(currentdir) to $(includedir),
               which in this example would be ../../../include)

另一个例子：

current dir = /home/username/projects/app/trunk/src/libs/libfoo/ 
destination = /home/username/projects/app/build/libfoo/ 
relative    = ../../../../build/libfoo

如何在尽可能便携的同时做到这一点？

Answer 1

Perl 是可移植的！这是使用核心 Perl 模块 File::Spec (resp. File::Spec::Functions) 中的 abs2rel 函数的解决方案：

current_dir= /home/username/projects/app/trunk/src/libs/libfoo/ 
destination= /home/username/projects/app/build/libfoo/ 
relative=    $(shell perl -MFile::Spec::Functions=abs2rel -E 'say abs2rel(shift, shift)' $(destination) $(current_dir))

makefile_target:
    @echo "Use now $(relative)"

Answer 2

Python 是可移植的！所以，我建议你在你的 submakefile 中使用这个简单的例子

使用current_dir 和destination_dir 路径os.path.relpath() 为您完成这项工作，因此您不必重新发明轮子。

submakefile.mk

current_dir=$(CURDIR)
makefile_target:
    (echo "import os"; echo "print(os.path.relpath('$(destination_dir)', '$(current_dir)'))" )| python

Answer 3

使用纯 Make 的强大的插入式解决方案：

override define \s :=
$() $()
endef

ifndef $(\s)
override $(\s) :=
else
$(error Defined special variable '$(\s)': reserved for internal use)
endif

override define dirname
$(patsubst %/,%,$(dir $(patsubst %/,%,$1)))
endef

override define prefix_1
$(if $(or $\
$(patsubst $(abspath $3)%,,$(abspath $1)),$\
$(patsubst $(abspath $3)%,,$(abspath $2))),$\
$(strip $(call prefix_1,$1,$2,$(call dirname,$3))),$\
$(strip $(abspath $3)))
endef

override define prefix
$(call prefix_1,$1,$2,$1)
endef

override define relpath_1
$(patsubst /%,%,$(subst $(\s),/,$(patsubst %,..,$(subst /,$(\s),$\
$(patsubst $3%,%,$(abspath $2)))))$\
$(patsubst $3%,%,$(abspath $1)))
endef

override define relpath
$(call relpath_1,$1,$2,$(call prefix,$1,$2))
endef

测试用例：

$(info $(call prefix,/home/user,/home/user))
$(info $(call prefix,/home/user,/home/user/))
$(info $(call prefix,/home/user/,/home/user))
$(info $(call prefix,/home/user/,/home/user/))

$(info $(call relpath,/home/user,/home/user))
$(info $(call relpath,/home/user,/home/user/))
$(info $(call relpath,/home/user/,/home/user))
$(info $(call relpath,/home/user/,/home/user/))

$(info ----------------------------------------------------------------------)

$(info $(call prefix,/home/user,/home/user/.local/share))
$(info $(call prefix,/home/user,/home/user/.local/share/))
$(info $(call prefix,/home/user/,/home/user/.local/share))
$(info $(call prefix,/home/user/,/home/user/.local/share/))

$(info $(call relpath,/home/user,/home/user/.local/share))
$(info $(call relpath,/home/user,/home/user/.local/share/))
$(info $(call relpath,/home/user/,/home/user/.local/share))
$(info $(call relpath,/home/user/,/home/user/.local/share/))

$(info ----------------------------------------------------------------------)

$(info $(call prefix,/home/user/.config,/home/user/.local/share))
$(info $(call prefix,/home/user/.config,/home/user/.local/share/))
$(info $(call prefix,/home/user/.config/,/home/user/.local/share))
$(info $(call prefix,/home/user/.config/,/home/user/.local/share/))

$(info $(call relpath,/home/user/.config,/home/user/.local/share))
$(info $(call relpath,/home/user/.config,/home/user/.local/share/))
$(info $(call relpath,/home/user/.config/,/home/user/.local/share))
$(info $(call relpath,/home/user/.config/,/home/user/.local/share/))

$(info ----------------------------------------------------------------------)

$(info $(call prefix,/home/user/.local/share,/home/user))
$(info $(call prefix,/home/user/.local/share,/home/user/))
$(info $(call prefix,/home/user/.local/share/,/home/user))
$(info $(call prefix,/home/user/.local/share/,/home/user/))

$(info $(call relpath,/home/user/.local/share,/home/user))
$(info $(call relpath,/home/user/.local/share,/home/user/))
$(info $(call relpath,/home/user/.local/share/,/home/user))
$(info $(call relpath,/home/user/.local/share/,/home/user/))

$(info ----------------------------------------------------------------------)

$(info $(call prefix,/home/user/.local/share,/home/user/.config))
$(info $(call prefix,/home/user/.local/share,/home/user/.config/))
$(info $(call prefix,/home/user/.local/share/,/home/user/.config))
$(info $(call prefix,/home/user/.local/share/,/home/user/.config/))

$(info $(call relpath,/home/user/.local/share,/home/user/.config))
$(info $(call relpath,/home/user/.local/share,/home/user/.config/))
$(info $(call relpath,/home/user/.local/share/,/home/user/.config))
$(info $(call relpath,/home/user/.local/share/,/home/user/.config/))

$(info ----------------------------------------------------------------------)

$(info $(call prefix,/root,/home/user))
$(info $(call prefix,/root,/home/user/))
$(info $(call prefix,/root/,/home/user))
$(info $(call prefix,/root/,/home/user/))

$(info $(call relpath,/root,/home/user))
$(info $(call relpath,/root,/home/user/))
$(info $(call relpath,/root/,/home/user))
$(info $(call relpath,/root/,/home/user/))

预期结果：

/home/user
/home/user
/home/user
/home/user




----------------------------------------------------------------------
/home/user
/home/user
/home/user
/home/user
../..
../..
../..
../..
----------------------------------------------------------------------
/home/user
/home/user
/home/user
/home/user
../../.config
../../.config
../../.config
../../.config
----------------------------------------------------------------------
/home/user
/home/user
/home/user
/home/user
.local/share
.local/share
.local/share
.local/share
----------------------------------------------------------------------
/home/user
/home/user
/home/user
/home/user
../.local/share
../.local/share
../.local/share
../.local/share
----------------------------------------------------------------------




../../root
../../root
../../root
../../root

Answer 4

shell 使用 realpath(1) 和 --relative-to 标志具有此功能，因此您只需调用 shell。

这是一个例子：

RELATIVE_FILE1_FILE2:=$(shell realpath --relative-to $(FILE1) $(FILE2))

您甚至可以通过一次调用 realpath(1) 来处理整个文件列表，因为它知道如何处理许多文件名。

这是一个例子：

RELATIVES:=$(shell realpath --relative-to $(RELATIVE) $(FILES))

Answer 5

这是一个仅使用 GNU make 函数的解决方案。尽管它是递归的，但它应该比调用外部程序更有效。这个想法非常简单：相对路径将是零或更多.. 到最常见的祖先，然后是一个后缀到第二个目录。困难的部分是在两条路径中找到最长的公共前缀。

# DOES not work if path has spaces
OneDirectoryUp=$(patsubst %/$(lastword $(subst /, ,$(1))),%,$(1))

# FindParentDir2(dir0, dir1, prefix)  returns prefix if dir0 and dir1
# start with prefix, otherwise returns
# FindParentDir2(dir0, dir1, OneDirectoryUp(prefix))
FindParentDir2=
$(if
  $(or
    $(patsubst $(3)/%,,$(1)),
    $(patsubst $(3)/%,,$(2))
   ),
   $(call FindParentDir2,$(1),$(2),$(call OneDirectoryUp,$(3))),
   $(3)
 )

FindParentDir=$(call FindParentDir2,$(1),$(2),$(1))

# how to make a variable with a space, courtesy of John Graham-Cumming 
# http://blog.jgc.org/2007/06/escaping-comma-and-space-in-gnu-make.html
space:= 
space+=

# dir1 relative to dir2 (dir1 and dir2 must be absolute paths)
RelativePath=$(subst
               $(space),
               ,
               $(patsubst
                 %,
                 ../,
                 $(subst
                   /,
                   ,
                   $(patsubst
                     $(call FindParentDir,$(1),$(2))/%,
                     %,
                     $(2)
                    )
                  )
                )
              )
             $(patsubst
               $(call FindParentDir,$(1),$(2))/%,
               %,
               $(1)
              )

# example of how to use (will give ..)
$(call RelativePath,/home/yale,/home/yale/workspace)

我最近将大量递归 makefile 转换为整个项目 make，因为众所周知，递归 make 不好，因为没有暴露整个依赖图 (http://aegis.sourceforge.net/auug97.pdf)。所有源代码和库路径都是相对于当前 makefile 目录定义的。我没有定义固定数量的通用 % 构建规则，而是为每个（源代码目录、输出目录）对创建了一组规则，这避免了使用 vpath 的歧义。创建构建规则时，我需要每个源代码目录的规范路径。虽然可以使用绝对路径，但它通常太长且可移植性较差（我碰巧使用的是 Cygwin GNU make，其中绝对路径具有 /cygdrive 前缀并且无法被 Windows 程序识别）。因此，我大量使用这个函数来生成规范路径。

Answer 6

Didier 的回答是最好的，但以下内容可能会给您一些想法：

includedir=/a/b/c/d
currentdir=/a/b/e/f/g
up=; while ! expr $includedir : $currentdir >/dev/null; do up=../$up; currentdir=`dirname $currentdir`; done; relative=$up`expr $includedir : $currentdir'/*\(.*\)'`
echo "up=$up  currentdir=$currentdir, relative=$relative"

排序！

（没有人说它必须漂亮......）

Answer 7

做你想做的事看起来并不容易。在 makefile 中使用很多组合的$(if 可能是可能的，但不便携（仅限 gmake）并且很麻烦。

恕我直言，您正在尝试解决您自己创建的问题。为什么不将includedir 的正确值作为顶级Makefile 的相对路径发送？它可以很容易地完成，如下所示：

rootdir = $(realpath .)
default:
    @$(MAKE) --directory=$(rootdir)/src/libs/libfoo includedir=../../../include

然后你可以在子makefiles中使用$(includedir)。它已经被定义为相对的。