关于Windows：Substring()失败-需要将结果强制转换为字符串而不是默认的double

Substring() fails - need to cast result as string instead of default double

在尝试之前，我认为子字符串很容易：

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# extract from a webpage with regex into $mmdd the value like 08/09
Write-Host $mmdd
08/09
$mmdd.Substring(0,2)

然后我得到：

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Method invocation failed because [System.Double] does not contain a method named 'Substring'.
At line:1 char:1
+ $test.Substring(0,2)
+ ~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : MethodNotFound

1	> $test.Substring(3)

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Method invocation failed because [System.Double] does not contain a method named 'Substring'.
At line:1 char:1
+ $test.Substring(3)
+ ~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : MethodNotFound

如何将变量$mmdd转换为字符串，以便可以在其上使用Substring()？

我怀疑我必须对以下内容做一些事情：

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$page | Select-String -Pattern $mmddyyyyRgx -AllMatches |
% { $_.Matches } |
% { $_.Value } |
Select-String -Pattern $mmddRgx -AllMatches |
% { $_.Matches } |
% { $_.Value } -Outvariable mmdd

因为$ mmdd给了我：

1	0.888888888888889

这是双重信号，无法像下面那样进行投射：

1	[string]$mmdd.Substring(0,2)

它将给我
0。
代替
08