Linux上目录的制作和上次修改时间 [英] Make and last modification times of directories on Linux

问题描述

考虑以下makefile:

Consider the following makefile:

foo :
    mkdir foo

foo/a.out : foo a.in
    cp a.in foo/a.out

foo/b.out : foo b.in
    cp b.in foo/b.out

及其随后的交互，从包含文件a.in和b.in的目录开始，并且没有其他内容:

and the following interaction with it, starting from a directory that contains files a.in and b.in and nothing else:

$ make foo/a.out
mkdir foo
cp a.in foo/a.out

到目前为止，很好.

$ make foo/b.out
cp b.in foo/b.out

仍然很好，但是现在:

$ make foo/a.out   # a.out should be up to date now!
cp a.in foo/a.out

即使未更改任何先决条件，它也会重建a.out目标.

It rebuilds the a.out target, even though none of its prerequisites have changed.

似乎正在发生的事情是，在创建foo/b.out时，目录foo的上次修改时间已更新，因此它将其视为已更改".

It seems like what's happening is that when foo/b.out is created, the last modification time of the directory foo is updated, so it picks that up as having "changed".

有办法避免这种情况吗?例如，是否有一种方法可以声明foo/a.out依赖于foo仅在于foo必须存在，并且在foo内部创建文件不会导致foo被认为已过时. ?

Is there a way to avoid this? For example, is there a way to declare that foo/a.out depends on foo only in that foo has to exist, and the creating of files inside foo doesn't cause foo to be considered out of date?

推荐答案

作为Make的权威最近指出:

永远不要做的一件事就是使用目录作为简单的先决条件.文件系统用来更新目录上修改时间的规则不适用于make."

但是我认为这会满足您的要求:

But I think this will do what you want:

foo :
    mkdir foo

foo/a.out : a.in | foo
    cp a.in foo/a.out

foo/b.out : b.in | foo
    cp b.in foo/b.out

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