Parameter Validation

To summarize Glenn Sizemore from the Scripting Guys blog, here is how you can validate your PowerShell parameters when you write your own script (requires V2):
Param(
[ValidateSet("Department", "AppData")][string]$type,
[ValidateRange(10, 25)][int]$size,
[ValidateScript({Test-connection $_ -count 2 -quiet})][string]$computername
)

And since version 3, the PowerShell ISE is smart enough (via Intellisense) to show you your choices in a drop-down for a ValidateSet parameter. 

Rounding Numbers

If you want to round numbers in PowerShell, then you have two choices (at least) with slightly different results.

Let's set the stage:
PS > $a = 8
PS > $b = 6
PS > $a / $b
1.3333333333333

One way is to use the format string approach.
 PS > "{0:n2}" -f ($a / $b)
1.33

So "{0:n2}" denotes a formatted string, where the 2 is how many decimal places to show.  After the -f, you put your expression to format.  There are other choices for this formatted string, which I will not detail here.  The point is that your output is a string.

Another way is to use the Math .NET class to Round.
PS > [Math]::Round(($a / $b), 2)
1.33

This time, however, you get a Double instead of a string. 

It looks like PowerShell does a great job at sorting number strings as numbers.  So far, it doesn't matter which way you use above; Sort-Object puts the numbers in the right order.  PowerShell even lets you do Math operations on numbers stored as strings!  Isn't it great?

New Hyper-V Virtual Machine with PowerShell

Here is the PowerShell for a new VM like the wizard does:
$vmName = "New Virtual Machine"
$vmPath = "C:\ProgramData\Microsoft\Windows\Hyper-V\"
New-VM -Name $vmName -Path "$vmPath\$vmName" -MemoryStartupBytes 512MB -NewVHDPath ` "$vmPath\$vmName\$vmName.vhdx" -NewVHDSizeBytes 127gb -Generation 1 -BootDevice CD
#new Gen 1 VM with files stored in $vmPath, with 512MB static RAM, with 1 CPU, with 127GB dynamic VHDX, #disconnected from network, with empty CD drive

Here is how to make other common configurations (one line at a time):
Set-VMDvdDrive -VMName $vmName -Path "k:\ISO\ISO.iso"; #add ISO file to existing drive
Set-VM -NewVMName $vmName -ProcessorCount 2 -DynamicMemory -MemoryMaximumBytes 4096MB #set dynamic memory and CPU
Set-VMNetworkAdapter -VMName $vmName -Name "SecretNet" #connect to network
Set-VM -NewVMName $vmName -AutomaticStartAction StartIfRunning -AutomaticStopAction ShutDown #change auto actions
Checkpoint-VM -Name $vmName #make a new snapshot/checkpoint

PowerShell Random Sort a List

Maybe you have a list that you want to put in a random order.  I had a list of words that I wanted shuffled without repeating.  At first, I was thinking that I'd have to devise some way of choosing at random without replacement, so that Get-Random wouldn't choose the same word twice.

Then I found that Get-Random has a -Count parameter, so I thought: could I make the count the same as the number of items on my list?

Of course!  Why did I even question?
"Mercury" , "Venus" , "Earth" , "Mars" , "Jupiter" , "Saturn" , "Uranus" , "Neptune" , "Pluto" | Get-Random  -Count  9

However, I did learn that the count cannot exceed the length of the list.  If it does, PowerShell won't complain; it will just stop when it has listed every item once.