Powershell/Regular Expression :- Get Host’s IP Address

Background

Quick follow-up to our past attempts at using Regular Expression to parse data within a lithe PowerShell Script.

Regular Expression

Positive Look Behind

  1. Regular-Expressions.Info
    • Lookahead and Lookbehind Zero-Length Assertions
      • Web Link
        Link
      • The construct for positive lookbehind is (?<=text): a pair of parentheses, with the opening parenthesis followed by a question mark, “less than” symbol, and an equals sign.
    • Regular Expression Reference: Special Groups
      • Web Link
        Link
      • Matches at a position if the pattern inside the lookbehind can be matched ending at that position.
      • Insight
        regular-expressions.info.positive.lookbehind.20190411.0825AM

Code

Powershell

Outline

  1. Get results of running IPConfig
    • Run IPConfig
    • Capture output in local variable
  2. Prepare Regular Expression
    • Look for IP Address
      • IPv4 Address Only

Regular Expression


(?<=IPv4 Address(\. )*): (\w*).(\w*).(\w*).(\w*)

Actual Code


Set-StrictMode -version 2
 
[string] $regExpPattern=$null;
[string] $inputString=$null;
[int]    $iNumberofMatches=0;
[object] $objList =$null;
[object] $objRegEx =$null;
[string] $objType = $null;
[int]    $iElementID = 0;
[string] $log=$null;
[string] $regExpOption=$null;
[Boolean] $debug = $false;
#[Boolean] $debug = $true;

[string]$domainName = $null;
[array]$domainList = $null;
[int] $domainListNumberofEntries=0;
[string]$topLevelDomain = $null;
[string]$secondLevelDomain = $null;
    
        
# Regular Expression
# Look for IPV4, once found get periods
#   look for 4 digits
# (?<=IPv4 Address(. )*): (\w*).(\w*).(\w*).(\w*)
$regExpPattern= "(?<="
$regExpPattern+= "IPv4 Address" 
$regExpPattern+= "(\. )*";
$regExpPattern+= ")";

$regExpPattern+= ":";
$regExpPattern+= " ";
$regExpPattern+= "(\w*).(\w*).(\w*).(\w*)";

# Regular Expression Option
$regExpOption="IgnoreCase";

# Run IP Config
$inputString = ipconfig

if ($debug)
{

    Write-Host;
    Write-Host;

    $log = "Input is {0} " -f $inputString;

    Write-Host($log);
   
    $log = "==========================================================================="
    Write-Host($log);

    Write-Host;
    
    
}

$log = "[regex]::expression is {0} " -f $regExpPattern;
Write-Host($log);


$objList = ( [regex]::matches( `
                                  $inputString `
                                , $regExpPattern `
                                , $regExpOption`
                             ) `
            )
 
if ($objList)
{
 
    if ($debug)
    {
         
        $objType = $objList.GetType();
 
        $log = "[regex]::matches return type is {0} " -f $objType;
 
        Write-Host($log);
 
    }
 
     
    $iNumberofMatches = $objList.Count;
    
    if ($debug)
    {   
 
        $log = "Number of Matches is {0}" -f $iNumberofMatches;
 
        Write-Host($log);
        
    }       
 
    #$objList;
    
    if ($iNumberofMatches -gt 0)
    {
 
        ForEach ($obj in $objList)
        {

            $ipAddress = $obj.Value;
        
            $log = "IP Address is {0}"  -f $ipAddress;
         
            Write-Host($log);
        
        }   
    }
 
 
}
else
{

	Write-Host "==================="
	$inputString
	Write-Host "==================="

    Write-Host "$objList is null"
}

Output

regex.regAhead.20190411.0145PM

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