将echo和cut命令分配给变量 [英] Assigning echo and cut command to a variable

问题描述

我正在尝试从 upper / lower / boo.txt中获取字符串 boo，并将其分配给变量。我正在尝试

I'm trying to get the string "boo" from "upper/lower/boo.txt" and assign it to a variable. I was trying

NAME= $(echo $WHOLE_THING | rev | cut -d "/" -f 1 | rev | cut -d "." -f 1)

，但结果为空。我在做什么错了？

but it comes out empty. What am I doing wrong?

推荐答案

不要那样做。使用内置的shell操作比使用诸如$codeut 和 rev 之类的进程外工具要有效得多。 。

Don't do it that way at all. Much more efficient is to use built-in shell operations rather than out-of-process tools such as cut and rev.

whole_thing=upper/lower/boo.txt
name=${whole_thing##*/}
name=${name%%.*}

请参见 BashFAQ＃100 获得有关bash中字符串操作的最佳做​​法的一般介绍，或有关参数扩展的bash黑客页面，以获取有关此处使用的技术的更集中参考。

See BashFAQ #100 for a general introduction to best practices for string manipulation in bash, or the bash-hackers page on parameter expansion for a more focused reference on the techniques used here.

现在，就您的原始代码无法正常工作的原因而言：

Now, in terms of why your original code didn't work:

var=$(command_goes_here)

...是正确的语法。相比之下：

...is the correct syntax. By contrast:

var= $(command_goes_here)

...在运行 command_goes_here var 的空环境变量>，然后在运行 command_goes_here 的输出作为其自己的命令时。

...exports an empty environment variable named var while running command_goes_here, and then while running the output of command_goes_here as its own command.

要显示另一个变体，

var = command_goes_here

...作为命令运行 var ，其中 = 作为其第一个参数，而 command_goes_here 作为其后一个参数。也就是说，空格很重要。 ：）

...runs var as a command, with = as its first argument, and command_goes_here as a subsequent argument. Which is to say, whitespace is important. :)

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