I'm trying to remove the first octet including the leading . from an IP address, I'm trying to use Regex but I cannot figure out the proper way to use it. Here is my code
'47.172.99.12' -split '\.(.*)',""
The result I want is
172.99.12
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4 Answers
The . character has a special meaning in a Regex pattern: it matches any character except a newline. You will need to escape it in order to match a literal period:
'47.172.99.12' -split '\.(.*)',""
^
Note however that this will return more results than you need:
PS > '47.172.99.12' -split '\.(.*)',""
47
172.99.12
PS >
To get what you want, you can index the result at 1:
PS > ('47.172.99.12' -split '\.(.*)',"")[1]
172.99.12
PS >
That said, using Regex for this task is somewhat overkill. You can simply use the String.Split method instead:
PS > '47.172.99.12'.Split('.', 2)[1]
172.99.12
PS >
2 Comments
Ansgar Wiechers
The
-split operator allows restricting the number of resulting elements too. You could do $head, $tail = '47.172.99.12' -split '\.', 2 (or $null, $tail = ... if you're not interested in the first octet).@AnsgarWiechers - True. But I meant more that Regex is inherently less efficient than the
Split method (albeit not by much in such a simple case). I don't like to use Regex solutions unless I need to match a variable pattern. For static text though, I prefer the built-in string methods.If you just want the 3 last numbers you can use the following regex :
(\.\d+){3}$
But if you want every things after the first dot you can use a positive look-behind :
(?<=\.).*
Comments
You can use the -replace operator instead of split:
'47.172.99.12' -replace '^\d+\.',""
Comments
I'm surprised, given the context, that no one mentioned the [ipaddress] class for this. Using this approach also ensures that the string is a valid IP Address.
$ipAddress = "192.168.0.1" -as [ipaddress]
If($ipAddress){
($ipAddress.GetAddressBytes())[1..3] -join "."
} Else {
Write-Host "Invalid Address"
}
-as will attempt to convert the string to [ipaddress]. If successful the cast is performed else $null is returned. Then we use .GetAddressBytes() to break the IP address into its 4 parts. Since we know at this point it is a valid IP then we can safely rejoin the last 3 parts with a period.
