从GNU Makefile调用`command -v find` [英] Calling `command -v find` from GNU Makefile

问题描述

我使用一个shell(bash，但我需要可移植性)和一个GNU Makefile.我有以下代码:

I use a shell (bash, but I need portability) and a GNU Makefile. I have this code:

check_commands:
        command -v find >/dev/null
        command -v asdf >/dev/null

如预期的那样，传递了第一个命令，第二个命令以错误中止了Makefile.现在，我删除了>/dev/null.为什么会这样

As supposed, the first command is passed, the second aborts the Makefile with an error. Now, I remove the >/dev/null. Why does then

check_commands:
        command -v find

产生以下错误?

make: command: Command not found.

推荐答案

从快速查看GNU make的源代码中的job.c来看，它试图避免在可能的情况下(即当命令行足够简单时)启动shell. (格式为cmd args，不带重定向，复合命令等)，而shell是默认外壳.那么问题是command是内置的，并且没有关联的可执行文件，因此来自make的错误消息.当您使用> /dev/null时，它不会发生，因为make认为该命令过于复杂，并将其留给sh来启动它.

Judging from a quick look at job.c in GNU make's sources, it attempts to avoid launching a shell when it can, i.e. when the command line is simple enough (of the form cmd args, without redirection, compound commands, etc.) and the shell is the default one. The issue is then that command is a built-in and does not have an associated executable, hence the error message from make. It does not occur when you have > /dev/null as make considers the command as too complicated and leaves it to sh to launch it.

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