Richard Siddaway's Blog

PowerShell SSH support is available by default in PowerShell v6.0 and later. The big thing for PowerShell v6.0 was SSH based remoting.

On Windows 10 / Server 2019 OpenSSH is available as an optional install. On earlier versions of Windows you need to install OpenSSH - https://github.com/PowerShell/openssh-portable

The installation instructions are available at

https://github.com/PowerShell/Win32-OpenSSH/wiki/Install-Win32-OpenSSH

If you’re still using Windows PowerShell and need SSH support consider

https://github.com/darkoperator/Posh-SSH

I think SSH remoting should be considered a must learn as its ideal for non-domain remoting situations and avoids the need for certificates in non-domain scenarios.

Count is a property on arrays

PS> $x = 1..10
PS> $x.Count
10

The same information is available through Length (which is the property in the System.Array class definition)

PS> $x.Length
10

If the variable is a scalar you get 1 returned

PS> $x = 1
PS> $x.Count
1

With an empty array you get zero returned

PS> $x = @()
PS> $x.Count
0

This means that however many items are in the array you can safely check the number of items.

Be careful with strings as Count and Length give different results

PS> $x = 'asdfghjkl;'
PS> $x.count
1
PS> $x.length
10

If you want to test the number of elements returned use Count rather than length

You have a few Where-Object options when you want to filter data. Remember that Where-Object filters objects based on property values and Select-Object filters objects based on object position in the pipeline or array as well as filtering properties.

The classic way to use Where-Object is to use a filter script

PS> Get-Process | Where-Object -FilterScript {$_.CPU -gt 5}

You’re filtering to accept process objects where the CPU property shows more than 5 seconds of usage

As an aside most people don’t use the FilterScript parameter they rely on positional parameters to assign the script block to FilterScript. Script analysers such as PSScriptAnalyzer (at least as far as the rules in VScode are concerned) don’t seem to object to the use of positional parameters in this case which is rather sloppy and remiss. Another reason I don’t like any of the analysis tools I’ve tried as they aren’t consistent.

PowerShell then introduced a simpler syntax

PS> Get-Process | Where-Object -Property CPU -gt -Value 5

which is usually used via positional parameters

PS> Get-Process | Where-Object CPU -gt 5

which again seems to sneak past the analysers. If you want multiple clauses in the filter using –and / –or to join them you have to use the original syntax. Also note that –gt isn’t an operator – its a parameter!

There is also the little used array method option to filter a collection of objects

PS> (Get-Process).Where({$_.CPU -gt 5})

which it should be noted is much faster than Where-Object on the pipeline.

When using Where-Object remember the options and if you’re using positional parameters remember what you’re actually doing.

File rename is a topic that seems to keep recurring.

The simple answer is that you use Rename-Item

PS> Rename-Item -Path C:\test\Newoutdata01.txt -NewName OldData01.txt

If for whatever bizarre reason you have a character such as [ in your file name the rename won’t work

PS> Rename-Item -Path C:\test\New[outdata02.txt -NewName OldData02.txt
Rename-Item : Cannot retrieve the dynamic parameters for the cmdlet. The specified wildcard character pattern is not valid: New[outdata02.txt
At line:1 char:1
+ Rename-Item -Path C:\test\New[outdata02.txt -NewName OldData02.txt
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidArgument: (:) [Rename-Item], ParameterBindingException
+ FullyQualifiedErrorId : GetDynamicParametersException,Microsoft.PowerShell.Commands.RenameItemCommand

The way round that is to use –LiteralPath

PS> Rename-Item -LiteralPath C:\test\New[outdata02.txt -NewName OldData02.txt

If you need to rename a bunch of files use Get-ChildItem and pipe the results into Rename-Item

There are incompatibilities between Powershell versions – you can’t use classes in Windows PowerShell v4 and there are differences between Windows PowerShell v5.1 and v6.x. One way to deal with PowerShell version incompatibilities is described in the recent post from the PowerShell team - https://devblogs.microsoft.com/powershell/using-psscriptanalyzer-to-check-powershell-version-compatibility/

I’m not a big fan of tools such as PSScriptAnalyzer as I find them restrictive and they get in the way of doing what I need to do. Having said that the usage described in the article is actually very useful especially the way you can configure which PowerShell versions you need to be worried about.

PSScriptAnalyzer is built into VSCode so the availability of the functionality to chaeck PowerShell version incompatibilities actually strengthens the case for using VSCode (I still don’t feel 100% comfortable with it – mainly because it does too much for what I need. The ISE is simpler and suits my needs better).

If you need work round PowerShell version incompatibilities in the code you write this may be of great help.

I saw a question on how to get wireless networks which got me thinking about string handling and working with legacy command line utilities. I also wanted to compare the options available in Windows PowerShell and PowerShell Core.

First up is a relatively brute force approach. This approach works is relatively easy to understand and maintain but isn’t very elegant.

function get-wlan {
[CmdletBinding()]
param()

$networks = netsh wlan show networks mode=bssid

$networks | Select-Object -Skip 4 |
Where-Object {$_ -ne ''} |
ForEach-Object {

if ($psitem.StartsWith('SSID')) {
$temp = $psitem -split ':'
Write-Verbose -Message $temp[1]
$network = $($temp[1].Trim())
}

if ($psitem.TrimStart().StartsWith('Authentication')){
$temp = $psitem -split ':'
Write-Verbose -Message $temp[1]
$authentication = $temp[1].Trim()
}

if ($psitem.TrimStart().StartsWith('Signal')){
$temp = $psitem -split ':'
Write-Verbose -Message $temp[1]
$signal = $temp[1].Trim()
}

if ($psitem.TrimStart().StartsWith('Radio type')){
$temp = $psitem -split ':'

$props = [ordered]@{
Network = $network
Authentication = $authentication
Type = $temp[1].Trim()
Signal = $signal
}
New-Object -TypeName PSobject -Property $props
}
}
}

Start by using netsh to get the wireless networks. Skip the first 4 lines (run the netsh command by itself to see what’s being skipped) and filter out blank lines (empty strings). For each line check if it’s of interest and if so split on the : character and take the data into a variable. On the radio type line create an object and output.