数组和-包含-测试数组元素中的子字符串 [英] Arrays and -contains - test for substrings in the elements of an array

问题描述

我正在尝试过滤掉特定组中的用户.

I am trying to filter out users that are in a specific group.

我在变量中得到以下输出: Group1 Group2 etc...

I got the following output in a variable: Group1 Group2 etc...

保存在数组中的每行的一组.我试图只过滤出一个特定的组.但是，当我使用-contains时，它总是说$false，即使该组在那里.

One group for each line saved in an array. Im trying to filter out only one specific group. But when I use -contains it always says $false, even tho the group is there.

我的代码:

$group = get-aduser -identity name -properties memberof |
  select-object -expandproperty memberof | %{ (get-adgroup $_).name }

$contains = $group -contains "string"

即使数组的元素包含字符串...，

$contains仍为$false.

$contains is $false even if the array has elements that contain the string...

我想念什么?

推荐答案

您的误解是您期望PowerShell的此答案以获取详细信息.

It looks like your misconception was that you expected PowerShell's -contains operator to perform substring matching against the elements of the LHS array.
Instead, it performs equality tests - as -eq would - against the array's elements - see this answer for details.

要针对数组的元素 执行文字子字符串匹配，请使用:

# With non-literal search strings:
[bool] $contains = $group -match ([regex]::Escape($someString))

# With a string literal that doesn't contain regex metachars.,
# escaping isn't needed.
[bool] $contains = $group -match 'foo'

# With a string literal with metachars., you must individually \-escape them.
[bool] $contains = $group -match 'foo\.bar'

注意:

• 上面显示了一种健壮的通用方法，可确保使用[regex]::Escape()将搜索字符串视为 literal 值，这是必需的，因为 -match期望输入一个 regex (常规表达式)作为其RHS(搜索模式).

• The above shows a robust, generic way of ensuring that your search string is treated as a literal value using [regex]::Escape(), which is necessary because -match expects a regex (regular expression) as its RHS (the search pattern).

转义并非总是必要的；具体来说，只有存在所谓的元字符(在正则表达式中具有特殊含义的字符，例如.)才需要它，并且在使用字符串 literal 时，您可以选择直接\-逃脱它们；例如，要搜索文字子字符串a.b，您可以传递'a\.b'.

Escaping isn't always necessary; specifically, only the presence of so-called metacharacters (those with special meaning in a regex, such as .) requires it, and when you're using a string literal, you can opt to directly \-escape them; e.g., to search for literal substring a.b, you can pass 'a\.b'.

• 有可能AD组名不需要转义，但重要的是要意识到一般的需要.

与PowerShell中的所有运算符一样，默认情况下，匹配不区分大小写 ；使用-cmatch变体进行区分大小写的匹配.

As with all operators in PowerShell, by default the matching is case-insensitive; use the -cmatch variant for case-sensitive matching.

上面约束的[bool]类型用于确保-match操作的结果转换为布尔值:

The [bool] type constrained above is used to ensure that the result of the -match operation is converted to a Boolean:

• -match直接返回带有标量(非数组)LHS的布尔值，而带有 array LHS的布尔值则充当过滤器，并返回匹配数组元素 ；在布尔上下文中(例如在if条件中)解释，通常仍能得到预期的结果，因为非空数组被解释为$true，而空数组则被解释为$false；再次，但是重要的是要知道区别.

• While -match directly returns a Boolean with a scalar (non-array) LHS, with an array LHS it acts as a filter, and returns the matching array elements instead; interpreted in a Boolean context, such as in an if conditional, that usually still gives the expected result, because a non-empty array is interpreted as $true, whereas an empty one as $false; again, however it's important to know the difference.

这在实践中很少会涉及性能，但是值得注意的是， -match由于用作数组的过滤器，总是与 all 数组匹配元素-一旦找到 first 匹配项，它就不会停止，就像-contains和-in运算符一样.

This will rarely be a performance concern in practice, but it is worth noting that -match, due to acting as a filter with arrays, always matches against all array elements - it doesn't stop once the first match is found, the way that the -contains and -in operators do.

• 从正面看，您可以使用-match本身获取匹配的元素.

• On the plus side, you can use -match to obtain the matching elements themselves.

对-contains执行 substring 匹配的错误期望可能是由于与名称相似但无关的

The mistaken expectation of -contains performing substring matching may have arisen from confusion with the similarly named, but unrelated String.Contains() method, which indeed performs literal substring matching; e.g., 'foo'.Contains('o') yields $true. Also note that .Contains() is case-sensitive by default.

PowerShell具有 no 运算符，用于 literal 子字符串匹配.

PowerShell has no operator for literal substring matching.

但是，您可以将PowerShell的通用数组过滤功能与.Contains()字符串方法结合使用-但请注意，这通常会(可能会)比-match方法更糟糕.

However, you could combine PowerShell's generic array-filtering features with the .Contains() string method - but note that this will typically perform (potentially much) worse than the -match approach.

合理执行的替代方法是使用PSv4 + .Where()数组方法，如下所示:

A reasonably performant alternative is to use the PSv4+ .Where() array method as follows:

# Note: Substring search is case-sensitive here.
[bool] $contains = $group.Where({ $_.Contains("string") }, 'First')

从好的方面来说，一旦找到第一个匹配项，此方法就会停止匹配.

On the plus side, this approach stops matching once the first match is found.

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