Problems pulling numbers in text string...

Question

Hi All,

I have a large array of string values, each of which are reasonably the same but I need to retrieve three digits which make up the VLAN id from a network adapter object

An example string is as follows:

Domain|TestDevGroup|IP-10.20.30.0-VL222-Ref

I have managed to create the following Regular expression: VL(.+)[0-9]{2,3}

This gives me the result 'VL222' which is near to what I want but does anyone know how I can select only the digits without the leading VL?

Also, I cant find out how I apply this query against an array string in PowerShell

for example if the network names were a single column in a .csv file:

$nics = import-csv nics.csv

foreach($nic in $Nics){

$Vlan = $nic | select-string -pattern 'VL(.+)[0-9]{2,3}'

}

Does not seem to work

Hopefully one of you can shed some light on a newb like me?

Many thanks guys,

Answer 1

Hi，

If you want to match the digits following VL, you could use zero-width positive lookbehind assertions and the regex could be (?<=VL)\d{2,3}

$nics = Import-Csv C:\nics.csv  
$Vlan = foreach($nic in $nics){  
if($nic.YourColumnName -match "(?<=VL)\d{2,3}"){$matches.Values}  
}  

https://learn.microsoft.com/en-us/dotnet/standard/base-types/grouping-constructs-in-regular-expressions#zero-width-positive-lookbehind-assertions

Best Regards,
Ian

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Answer 2

Maybe something like this?

$nic = "Domain|TestDevGroup|IP-10.20.30.0-VL222-Ref"
$vlan = ($nic -split("-") -replace "VL","")[2]
$vlan

$vlan contains "222"

And this is the foreach piece (not tested):

$nics = import-csv nics.csv
foreach($nic in $nics){
       $vlan = ($nic -split("-") -replace "VL","")[2]
       $vlan
       }

---

(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)

Regards
Andreas Baumgarten

Answer 3

If you're going to ask the same question in multiple places, please have the curtesy to leave a link to the other question!
problems-pulling-numbers-in-text-string
I answered your question in the "Scripting Guys" forum.

Your regex is incorrect. It matches the 1st character after "VL" and "memorizes" it (because it in a group), and them matches the next two digits -- but it will also match the next three -- so it'll also match "VL2222". That's not what you want.

$s = "Domain|TestDevGroup|IP-10.20.30.0-VL222-Re"
$s -match "VL(.+)[0-9]{2,3}"
True

$matches

Name                           Value
----                           -----
1                              2
0                              VL222

The regex that does what you ask is "-VL(\d\d\d?)-", which uses the hyphens as a sort of anchor. That's not entirely necessary, but it adds a bit of certainty to the outcome.

$s = "Domain|TestDevGroup|IP-10.20.30.0-VL222-Re"
$VLAN = $null
if ($s -match "-VL(\d\d\?)-"){
    $VLAN = $matches[1]
}

To extract the string you want from a CSV, try this:

import-csv nics.csv |
    Foreach-Object{
        $Vlan = $null
        if ($_.COLUMNNAME -match '-VL(\d\d\d?)-'){
            $Vlan = $matches[1]
        }
        etc.
        etc.
}