md5sum fails to find file after changing dir in a Makefile instruction

问题

I am having trouble generating a package with a md5sum of the contained files using Makefiles.

I do have found an workaround, but I am not satisfied with it.

This is a example of how my makefile works, it can be used to reproduce my problem with file1, and my workaround with file2.

    VERSION:=1
    DIR:=tmp

    file: #rule to build the file with current version tag
            touch $(DIR)/file-$(VERSION)

    $(DIR)/file1.tar:file #rule that fails to create the md5 file
            cd $(DIR)
            md5sum -b \
                    file-$(VERSION) \
                    >> file-$(VERSION).md5
            tar -cf $@ \
                    file-$(VERSION) \
                    file-$(VERSION).md5
            cd -

    $(DIR)/file2.tar:file #workaround that fails to create the md5 file
            md5sum -b \
                    $(DIR)/file-$(VERSION) \
                    >> $(DIR)/file-$(VERSION).md5
            tar -cf $@ -C $(DIR) \
                    file-$(VERSION) \
                    file-$(VERSION).md5

    file1: $(DIR) $(DIR)/file1.tar

    file2: $(DIR) $(DIR)/file2.tar

    $(DIR):
            mkdir -p $(DIR)

Running file1, the build fails and I get the following output:

:~/tmp$ make file1
mkdir -p tmp
touch tmp/file-1
cd tmp
md5sum -b \
    file-1 \
    >> file-1.md5
md5sum: file-1: No such file or directory
Makefile:8: recipe for target 'tmp/file1.tar' failed
make: *** [tmp/file1.tar] Error 1

Running file2, the file is built successfully:

:~/tmp$ make file2
touch tmp/file-1
md5sum -b \
    tmp/file-1 \
    >> tmp/file-1.md5
tar -cf tmp/file2.tar -C tmp \
    file-1 \
    file-1.md5

My question is, why md5sum tool fails to find the file in the same dir as it is running after calling cd dir when it is used as a Makefile instruction? Or, what I am missing?

回答1:

Each line in a recipe is executed by a separate shell invocation. So your cd $(DIR) line is executed by a shell and has no effect on the next line (md5sum...) that gets executed by another shell. In your case a simple solution consists in chaining all commands such that they are considered as a single line by make and executed by the same shell:

target: prerequisites
    cd here; \
    do that; \
    ...

or:

target: prerequisites
    cd here && \
    do that && \
    ...

来源：https://stackoverflow.com/questions/49493821/md5sum-fails-to-find-file-after-changing-dir-in-a-makefile-instruction

标签

makefile

md5sum