Process input [string] line-by-line in PowerShell

Question

I am writing a function to convert a list of IP addresses from their dotted-decimal form to an unsigned integer in PowerShell. Here is my function:

function Convert-IPtoInteger() {

    param(
        [Parameter(Mandatory=$true, Position=0, ParameterSetName="IP Address",
            ValueFromPipeline=$true, ValueFromPipelineByPropertyName=$true)]
        [string] $addresses
    )

    process {
        foreach ($ip in $addresses) {
            if ($ip -match '(\d\d?\d?\.){3}\d\d?\d?') { # approximate regex, matches some impossible addresses like 999.0.0.0
                $s = "$ip".Split(".");
                [uint32] $x = 0;
                (0..3) | ForEach-Object { # positions 0, 1, 2, 3 in previous string
                    $x = $x -shl 8; # bit shift previous value to the left by 8 bits
                    $x += $s[$_];
                }
                Write-Output $x;
            }
        }
    }
}

I had tried this with $addresses declared as a scalar as shown and as a [string[]] array. In both cases, piping a string of multiple lines (created with shift-enter) causes an error after the first element. If I use the Get-Content command to read the same text from a file the program completes as expected.

PS C:\...\1> $example = "192.168.1.1
192.168.2.1"

PS C:\...\1> $example | Convert-IPtoInteger
Cannot convert value "1
192" to type "System.UInt32". Error: "Input string was not in a correct format."
At C:\...\.ps1:16 char:18
+                     $x += $s[$_];
+                     ~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvalidCastFromStringToInteger

3232235776

PS C:\...\1> $example > example.txt

PS C:\...\1> Get-Content .\example.txt | Convert-IPtoInteger
3232235777
3232236033

I believe that the difference is how PowerShell is handling newlines. Line 16 ($x += $s[$_]) appears to be reading "1`n192" in the same token, rather than receiving each element as a separate $ip from the foreach statement.

The Get-Member command shows that $example | Get-Member is an instance of System.String just like Get-Content .\example.txt | Get-Member.

I would like for my program to correctly accept input from text files and also from strings. What am I missing here? Why is Get-Content being parsed differently from a multi-line string?

Owain Esau · Accepted Answer · 2018-03-01 04:42:48Z

Put the IP Addresses in an object array:

$example = @("192.168.1.1", "192.168.2.1")
$example | convert-IPtointeger

result:

3232235777 
3232236033

The reason it is different is because you are using Foreach-Object against a string:

$example1 = @("192.168.1.1", "192.168.2.1") 
$example1.GetType()

$example2 = "192.168.1.1
192.168.2.1"
$example2.GetType()

$example3 = (Get-Content "C:\Users\owain.esau\Desktop\links.txt" )
$example3.GetType()

This returns the following

IsPublic IsSerial Name                                     BaseType                                                                                                                                                                          
-------- -------- ----                                     --------                                                                                                                                                                          
True     True     Object[]                                 System.Array                                                                                                                                                                      
True     True     String                                   System.Object                                                                                                                                                                     
True     True     Object[]                                 System.Array

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