Powershell script and subst command

Question

I have the following permissions: 2.0 script:

function getFreeDrive { [char[]]$driveLetters = @([char]'E'..[char]'Z') foreach ($d in $driveLetters) { if(!(Test-Path -Path "$d`:" -IsValid)) { return $d } } } $drive = getFreeDrive subst "$drive`:" T:\temp ls "$drive`:\" # just a dummy command subst "$drive`:" /D 

I want a script

• find the first unused drive letter
• create a new disk using subst
• do something on this disc.
• delete the disk with subst

The script works fine when I run it the first time. If I run the script a second time in the same shell, I get an error message from the ls command saying that the drive was not found. If I open a new shell and run the script, it works fine again.

What is the problem with my script and how can I make it work several times in the same powershell instance?

Or maybe there is an alternative to subst ? I tried using the powershell drive, but it does not work with other Windows programs (for example, devenv.exe).

Answer 1

I can replicate the same behavior as you, even until the moment when in one Powershell window I can’t even burn a CD to the created disc, but if I open a completely new window, I can handle it just fine.

The behavior is as shown here:

http://social.technet.microsoft.com/Forums/en-US/winserverpowershell/thread/2e414f3c-98dd-4d8b-a3a3-88cfa0e7594c/

The workaround is probably to use PSDrive, as mentioned above, or just not display, then turn it off and then try to reassign the same drive in the same session.

Answer 2

An alternative is to use PSProviders and more specifically PSDrives (see get-help about_providers ):

 PS > New-PSDrive -Name "tr" -PSProvider filesystem -Root "c:\temp" Name Used (GB) Free (GB) Provider Root ---- --------- --------- -------- ---- tr 28,15 FileSystem C:\temp PS > ls tr:*.c Répertoire : C:\temp Mode LastWriteTime Length Name ---- ------------- ------ ---- -a--- 01/08/2012 05:28 994 test.c PS > Remove-PSDrive -Name "tr" 

The problem is that these disks cannot be used with the explorer.exe shell.

Answer 3

I had the same problem and my workaround - note that I am using version 3 - is calling Get-PSDrive before moving to a newly connected drive:

 $drive = getFreeDrive subst "$drive`:" T:\temp Get-PSDrive | Out-Null ls "$drive`:\" # just a dummy command subst "$drive`:" /D