从IPv4地址的字符串表示形式获取特定的八位位组 [英] Get a specific octet from the string representation of an IPv4 address

问题描述

我有一个名为$Ip的变量.该变量在内部具有类似于"172.13.23.34"的IP.我想获取第三个八位位组或172.13之间的下一个字符.和.34(在这种情况下为字符串数字23)，并存储在另一个变量中，以使用以下命令设置VLANID.

I have a variable named $Ip. This variable has an IP inside like "172.13.23.34". I would like to get the 3rd octet or the next character between 172.13. and .34 which is a string number 23 in this case and store in another variable to set up a VLANID with the command below.

$Ip = 172.13.23.34
$VLANID = ?
Set-Netadapter -Name "Ethernet" -VlanID $VLANID

如何获取此特定信息?

推荐答案

While -split, the regex-based string-splitting operator, or the literal-substring-based Split() method are the proper tools for splitting a string into tokens by separators in general, there's an easier solution in your case:

# Trick: [version] splits the string into its numerical components.
#        The .Build property value corresponds to the 3rd octet.
PS> ([version] '172.13.23.34').Build
23

[version](System.Version)类型，用于版本号，可以理解由.分隔的4个组件编号，它们看起来像IPv4地址.此类实例的属性映射到IPv4地址的八位字节，如下所示:

The [version] (System.Version) type, intended for version numbers, understands 4-component numbers separated by ., which look like IPv4 addresses. The properties of such instances map onto the octets of an IPv4 address as follows:

• .Major ...第一个八位位组(172)
• .Minor ...第二个八位位组(13)
• .Build ...第三个八位位组(23)
• .Revision ...第四字节(34)

• .Major ... 1st octet (172)
• .Minor ... 2nd octet (13)
• .Build ... 3rd octet (23)
• .Revision ... 4th octet (34)

注意:

• 如果需要所有个八位位组，请考虑 iRon的有用答案，其中正确使用[IPAddress]类型.

• If you need all octets, consider iRon's helpful answer, which more properly uses the [IPAddress] type.

也就是说，[version]比[IPAddress]具有一个优势:它实现了 System.IComparable 接口，这意味着您比较 IPv4地址；例如，
[version] '172.9.23.34' -lt [version] '172.13.23.34'是$true

That said, [version] has one advantage over [IPAddress]: it implements the System.IComparable interface, which means that you compare IPv4 addresses; e.g.,
[version] '172.9.23.34' -lt [version] '172.13.23.34' is $true

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