Find Available Drive Letter and Change - powershell

Question

I am trying to create a PowerShell script that will find an available drive letter, map a network drive, and then change to that mapped drive. I found the following which mapped \\server\share as the D: drive:
$Drive = New-PSDrive -Name $(for($j=67;gdr($d=[char]$J++)2>0){}$d) -PSProvider FileSystem -Root \\server\share\
I can manually enter D:, but how can I change this in a script? I was thinking along the lines of this:
$Drive = $Drive.Trim(":")
But the statement above throws the following error:
Method invocation failed because [System.Management.Automation.PSDriveInfo] does
not contain a method named 'Trim'.
At line:1 char:1
+ $Drive = $Drive.Trim(":")
+ ~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : MethodNotFound

Answer 1

You could check a list of potential drive letters against the list of currently assigned drive letters and use the first unused one:
$used = Get-PSDrive | Select-Object -Expand Name |
Where-Object { $_.Length -eq 1 }
$drive = 90..65 | ForEach-Object { [string][char]$_ } |
Where-Object { $used -notcontains $_ } |
Select-Object -First 1
New-PSDrive -Name $drive -PSProvider FileSystem -Root \\server\share
Set-Location "${drive}:"
or a random one from that list:
$used = Get-PSDrive | Select-Object -Expand Name |
Where-Object { $_.Length -eq 1 }
$unused = 90..65 | ForEach-Object { [string][char]$_ } |
Where-Object { $used -notcontains $_ }
$drive = $unused[(Get-Random -Minimum 0 -Maximum $unused.Count)]
New-PSDrive -Name $drive -PSProvider FileSystem -Root \\server\share
Set-Location "${drive}:"

Answer 2

The functions used in Ansgar's answer are likely returning the DVD/CD drive because it has no media in it. To get a free drive letter, that is likely* not the CD/DVD drive we search from i-z:
$dl=ls function:[i-z]: -n | ?{ !(test-path $_) } |select -last 1