bash bash中括号${}、$()、$[]的区别和用法
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Brackets ${}, $(), $[] difference and usage in bash
提问by yart
Bash contains different braces and they used differently. Could you please explain comprehensively what is difference between ${}, $()and $[]?
Where they are used in bash? What is their main purpose?
Bash 包含不同的大括号，它们的用法也不同。您能否全面解释一下${},$()和之间的区别$[]？它们用于 bash 的哪些地方？他们的主要目的是什么？
回答by user1146332
The keyword is shell expansion! So i highly recommend you to read the section Shell Expansionsin your bash reference manual.
关键词是shell expansion！所以我强烈建议您阅读Shell Expansionsbash 参考手册中的部分。
You can access this section online [1].
您可以在线访问此部分 [1]。
The names of the following stated forms are:
下列表格的名称是：
${}Parameter expansion$()Command substitution
${}参数扩展$()命令替换
the form $[]isn't actually stated in the manual so i wouldn't use it.
该表格$[]实际上并未在手册中说明，所以我不会使用它。
[1] http://www.gnu.org/software/bash/manual/bashref.html#Shell-Expansions
[1] http://www.gnu.org/software/bash/manual/bashref.html#Shell-Expansions
