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GNU make：“无需对“目标”执行任何操作；与“目标”相比是最新的ÉD;

发布于 2024-11-02 23:33:18 字数 86 浏览 1 评论 0原文

GNU 如何决定发出哪些消息？我使用的 Makefile 导致当目标更新时，不对“目标”消息执行任何操作。但我认为“目标”是最新的会更合适。

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探春 2024-11-09 23:33:18

主要区别在于 gmake 是否有构建目标的规则。如果目标没有规则，但目标存在，那么 gmake 会说，“没什么可做的”，例如，“我不知道如何更新这个东西，但它已经存在，所以我猜有无事可做。”如果有规则，但目标已经是最新的，那么 gmake 会说“是最新的”，例如“我确实有更新这个东西的说明，但它似乎已经是最新的 -到目前为止，所以我不会做任何事情。”

这是一个具体的例子：

$ echo "upToDate: older ; @echo done" > Makefile
$ touch older ; sleep 2 ; touch upToDate ; touch nothingToDo
$ ls --full-time -l older upToDate nothingToDo
-rw-r--r-- 1 ericm ericm 0 2011-04-20 11:13:04.970243002 -0700 nothingToDo
-rw-r--r-- 1 ericm ericm 0 2011-04-20 11:13:02.960243003 -0700 older
-rw-r--r-- 1 ericm ericm 0 2011-04-20 11:13:04.960243001 -0700 upToDate
$ gmake upToDate
gmake: `upToDate' is up to date.
$ gmake nothingToDo
gmake: Nothing to be done for `nothingToDo'.

由于 gmake 没有“nothingToDo”规则，但文件已经存在，因此您会收到“nothing to be do”消息。如果“nothingToDo”不存在，您将收到熟悉的“无规则可制定”消息。

相反，由于 gmake 有“upToDate”规则，并且文件看起来是最新的，因此您会收到“is up to date”消息。

The chief difference is in whether gmake has a rule to build the target or not. If there is no rule for the target, but the target exists, then gmake will say, "Nothing to be done", as in, "I don't know how to update this thing, but it already exists, so I guess there's nothing to be done." If there is a rule, but the target is already up-to-date, then gmake will say, "is up to date", as in, "I do have instructions for updating this thing, but it appears to already be up-to-date, so I'm not going to do anything."

Here's a concrete example:

$ echo "upToDate: older ; @echo done" > Makefile
$ touch older ; sleep 2 ; touch upToDate ; touch nothingToDo
$ ls --full-time -l older upToDate nothingToDo
-rw-r--r-- 1 ericm ericm 0 2011-04-20 11:13:04.970243002 -0700 nothingToDo
-rw-r--r-- 1 ericm ericm 0 2011-04-20 11:13:02.960243003 -0700 older
-rw-r--r-- 1 ericm ericm 0 2011-04-20 11:13:04.960243001 -0700 upToDate
$ gmake upToDate
gmake: `upToDate' is up to date.
$ gmake nothingToDo
gmake: Nothing to be done for `nothingToDo'.

Since gmake has no rule for "nothingToDo", but the file already exists, you get the "nothing to be done" message. If "nothingToDo" did not exist, you would instead get the familiar, "No rule to make" message.

In contrast, because gmake has a rule for "upToDate", and the file appears to be up-to-date, you get the "is up to date" message.

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