$($error[0])和$error[0]的区别

$()这种写法的主要区别体现在字符串中，单独运行的确没有区别。
比如字符串 “$error[0]”，输出的并不是最后一个error，而是所有的error。因为语法解析器只会解析到$error，后面的【0】是不会解析的。$()的诞生主要是为了解决这个问题。比如字符串“$($error[0])”是会把$()内部的语句当成一个完整的表达式，先运行，运行结束后再替换到字符串中。
 

PS> dir pstips.net
dir : Cannot find path 'D:\Users\bzli\pstips.net' because it does not exist.
At line:1 char:1
+ dir pstips.net
+ ~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (D:\Users\bzli\pstips.net:String) [Get-ChildItem], ItemNotFoundException
    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetChildItemCommand

PS> 1/0
Attempted to divide by zero.
At line:1 char:1
+ 1/0
+ ~~~
    + CategoryInfo          : NotSpecified: (:) [], RuntimeException
    + FullyQualifiedErrorId : RuntimeException

PS> "$error[0]"
Attempted to divide by zero. Cannot find path 'D:\Users\bzli\pstips.net' because it does not exist. The specified module
 'PSReadline' was not loaded because no valid module file was found in any module directory.[0]
PS> "$($error[0])"
Attempted to divide by zero.