Makefile`echo -n'不起作用 [英] Makefile `echo -n' not working

问题描述

我试图让我的Makefile回显文本而没有结尾的换行符，但是无法这样做.我在OS X上遇到了这种情况(在Linux上，一切正常.)

I am trying to have my Makefile echo text without the trailing new line, but am unable to. I am experiencing the behavior on OS X (on Linux everything works as expected).

a:
    @echo -n "hello"

b:
    @echo -n hello

c:
    @/bin/echo -n "hello"

输出:

$make a
-n hello
$make b
hello$make c
hello$

换句话说，make a被破坏了.到底是怎么回事? make是否使用内置回显?显然，双引号的出现改变了行为，但是为什么呢?

In other words, the make a is broken. What exactly is happening? Is make using a built-in echo? Clearly the presence of the double quotes changes the behavior, but why?

由@chepner发现，使用makefile中/bin/echo的完整路径可以正确理解-n标志.

As discovered by @chepner, using the full path to /bin/echo in the makefile understands the -n flag correctly.

推荐答案

有关引号的某些内容使make感到困惑.您的代码对我而言的行为相同，但以下各项按预期工作:

Something about the quotes confuses make. Your code behaves the same for me, but the following works as expected:

help:
        @echo -n Shouldn\'t print a newline

硬编码可执行文件的路径也可以:

Hardcoding the path to the executable also works:

help:
        @/bin/echo -n "Shouldn't print a newline"

用于echo的Mac OS X手册页在讨论外壳内置echo的存在时，提到sh(1)的echo不支持-n选项，但是失败了.向我解释(无论如何)为什么我的第一个替代方法有效.

The Mac OS X man page for echo, while discussing the existence of shell built-in echos, mentions that the echo of sh(1) does not support the -n option, but that fails to explain (to me, anyway) why my first alternative works.

确认make在默认情况下正在使用sh执行命令.在

Confirmation that make is using sh to execute the commands by default. In

SHELL = bash
help:
        @echo -n "Shouldn't print a newline"
        @echo -n Shouldn\'t print a newline

两个echo语句的行为相同(不打印换行符).因此，如果没有该变量，我们将bash假装为sh，但是对两行的评估不同.问题1:为什么?问题2:第二行是本地bash回声还是/bin/echo，而不是模拟的sh echo?

both echo statements behave the same (no newlines printed). So without that variable, we have bash pretending to be sh, but evaluating the two lines differently. Question 1: why? Question 2: is the second line the native bash echo or /bin/echo, rather than the emulated sh echo?

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