Get-DotNetFrameworkVersions.ps1

<#
.SYNOPSIS
Determine which .NET Frameworks are installed on the requested system.

.OUTPUTS
System.Collections.Hashtable of semantic version names to version numbers
of .NET frameworks installed.

.FUNCTIONALITY
DotNet

.COMPONENT
Microsoft.Win32.RegistryKey

.EXAMPLE
Get-DotNetFrameworkVersions.ps1

Name                           Value
----                           -----
v4.6.2+win10ann                4.6.1586
v3.5                           3.5.30729.4926
v2.0.50727                     2.0.50727.4927
v3.0                           3.0.30729.4926
#>

#Requires -Version 3
[CmdletBinding()][OutputType([hashtable])] Param(
# The computer to list the installed .NET Frameworks for.
[Alias('CN','Server')][string]$ComputerName = $env:COMPUTERNAME
)

function Add-Version([string]$Name,[string]$Version)
{if($Version){@{$Name=[version]$Version}}else{@{}}}

$hklm = [Microsoft.Win32.RegistryKey]::OpenRemoteBaseKey('LocalMachine',$ComputerName)
$ndp = $hklm.OpenSubKey('SOFTWARE\Microsoft\NET Framework Setup\NDP')

$versions = @{}
# get v1-v3.x
$ndp.GetSubKeyNames() |
	Where-Object {$_ -like 'v[123].*'} |
	ForEach-Object {
		$k = $ndp.OpenSubKey($_)
		$v = $k.GetValue('Version')
		Write-Verbose "Found '$_' subkey, version $v"
		$versions += Add-Version $_ $v
		[void]$k.Dispose(); $k = $null
	}

# get v4.x
$v4 = $ndp.OpenSubKey('v4\Full')
try
{
	[string]$release = $v4.GetValue('Release')
	Write-Verbose "v4 release $release"
	$name = [ordered]@{ # see https://msdn.microsoft.com/en-us/library/hh925568.aspx
		'528049' = 'v4.8'
		'528372' = 'v4.8+win10may2020'
		'528040' = 'v4.8+win10may2019'
		'461814' = 'v4.7.2'
		'461808' = 'v4.7.2+win10april2018'
		'461310' = 'v4.7.1'
		'461308' = 'v4.7.1+win10fcu'
		'460805' = 'v4.7'
		'460798' = 'v4.7+win10cu'
		'394806' = 'v4.6.2'
		'394802' = 'v4.6.2+win10ann'
		'394748' = 'v4.6.2-preview'
		'394747' = 'v4.6.2-preview'
		'394271' = 'v4.6.1'
		'394254' = 'v4.6.1+win10'
		'393297' = 'v4.6'
		'393295' = 'v4.6+win10'
		'379893' = 'v4.5.2'
		'378758' = 'v4.5.1'
		'378675' = 'v4.5.1+win8.1'
		'378389' = 'v4.5'
	}
	foreach($key in $name.Keys)
	{
		if($release -ge $key)
		{
			$versions += Add-Version $name.$key $v4.GetValue('Version')
			break
		}
	}
}
catch [ArgumentNullException]
{
	Write-Warning "Unable to open the version 4 sub key."
}
finally
{
	if($v4) {[void]$v4.Dispose(); $v4 = $null}
	[void]$hklm.Dispose(); $hklm = $null
	[void]$ndp.Dispose(); $ndp = $null
}

$versions