bash 内联命令
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bash for inline command
提问by dale
I have to run commands, in a bash script, and within this bash script I have to run other commands. I am running CentOS.
我必须在 bash 脚本中运行命令，并且在这个 bash 脚本中我必须运行其他命令。我正在运行 CentOS。
I found 2 ways to do this on blogs and manuals:
我在博客和手册上找到了两种方法：
1) using the ticks or accent char
1) 使用刻度或重音字符
command `sub command`
or
或者
2) using the dollar sign and parentheses
2) 使用美元符号和括号
command $(sub command)
What is the difference between the 2 and which one is preferable to use?
2 和哪个更适合使用之间有什么区别？
回答by holygeek
There's no difference except in "nestability":
除了“可嵌套性”之外没有区别：
The $()is nestable:
该$()是嵌套：
$ echo $(echo "hi" $(echo "there"))
while the `` is not.
而``不是。
回答by Gordon Davisson
Others have pointed out the difference in syntax (basically, $()is slightly cleaner wrt nesting and escapes), but nobody's mentioned what I consider the more important difference: $()is much easier to read. It doesn't look like single-quotes (which mean something totally different), and the opening and closing delimiters are different, making it easier to visually distinguish its contents.
其他人指出了语法上的差异（基本上，$()嵌套和转义稍微干净一点），但没有人提到我认为更重要的区别：$()更容易阅读。它看起来不像单引号（这意味着完全不同的东西），并且开始和结束分隔符不同，更容易在视觉上区分其内容。
For your own scripts, this may not be really critical; code readability is good, but functionality is more important. But for anyone writing tutorials, sample code, stackoverflow answers, etc, readability is much more important. People willtype single-quotes instead of backquotes when typing in examples, etc, and then get confused when it doesn't work as expected.
对于您自己的脚本，这可能并不重要；代码可读性好，但功能更重要。但是对于任何编写教程、示例代码、stackoverflow 答案等的人来说，可读性更为重要。人们在输入示例等时会输入单引号而不是反引号，然后当它没有按预期工作时会感到困惑。
So for everyone writing examples on stackoverflow: please save your readers some trouble, and always use the $()form.
因此，对于在 stackoverflow 上编写示例的每个人：请为您的读者省去一些麻烦，并始终使用$()表格。
回答by duskwuff -inactive-
$(...)and backticks are very similar. The only difference between the two is some details of what special characters are substituted in them; the manual explains better than I could:
$(...)和反引号非常相似。两者之间的唯一区别是其中替换了哪些特殊字符的一些细节；手册比我能解释的更好：
When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by $, `, or . The first backquote not preceded by a backslash terminates the command substitution. When using the $(command) form, all characters between the parentheses make up the command; none are treated specially.
当使用旧式反引号替换形式时，反斜杠保留其字面意义，除非后跟 $、` 或 。前面没有反斜杠的第一个反引号终止命令替换。使用 $(command) 形式时，括号之间的所有字符组成命令；没有被特殊对待。
This makes it a bit easier to nest $(...), for instance. Besides that, though, there's no difference.
例如，这使得嵌套更容易$(...)一些。不过除此之外，没有什么区别。
回答by another.anon.coward
Quoting from http://tldp.org/LDP/abs/html/commandsub.html:
引自http://tldp.org/LDP/abs/html/commandsub.html：
- The $(...) form of command substitution treats a double backslash in a different way than `...`.
- The $(...) form of command substitution permits nesting
- $(...) 形式的命令替换以不同于 `...` 的方式处理双反斜杠。
- $(...) 形式的命令替换允许嵌套
Hope this helps!
希望这可以帮助！
回答by Grasshopper
I must agree with Gordon in the fact that $() is way cleaner. I struggled for 2 hours editing my .bash_profile to add homebrew bash completion only to find that I should've been using ` and not '.
我必须同意 Gordon 的观点，即 $() 更干净。我努力了 2 个小时来编辑我的 .bash_profile 以添加自制的 bash 完成，结果发现我应该一直使用“而不是”。
