Powershell Try Catch IOException DirectoryExist - powershell

Question

I'm using a power shell script to copy some files from my computer to a USB drive. However, even though I'm catching the System.IO exception, I still get the error at the bottom. How do I properly catch this exception, so it shows the message in my Catch block.
CLS
$parentDirectory="C:\Users\someUser"
$userDirectory="someUserDirectory"
$copyDrive="E:"
$folderName="Downloads"
$date = Get-Date
$dateDay=$date.Day
$dateMonth=$date.Month
$dateYear=$date.Year
$folderDate=$dateDay.ToString()+"-"+$dateMonth.ToString()+"-"+$dateYear.ToString();
Try{
New-Item -Path $copyDrive\$folderDate -ItemType directory
Copy-Item $parentDirectory\$userDirectory\$folderName\* $copyDrive\$folderDate
}
Catch [System.IO]
{
WriteOutput "Directory Exists Already"
}
New-Item : Item with specified name E:\16-12-2014 already exists.
At C:\Users\someUser\Desktop\checkexist.ps1:15 char:9
+ New-Item -Path $copyDrive\$folderDate -ItemType directory
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ResourceExists: (E:\16-12-2014:String) [New-Item], IOException
+ FullyQualifiedErrorId : DirectoryExist,Microsoft.PowerShell.Commands.NewItemCommand

Answer 1

If you want to catch an exception for a New-Item call, you need to do two things:
Set $ErrorActionPreference = "Stop" by default its value is Continue. This will make the script Stop in case of exceptions.
Trap the correct exception and/or all of them
if you want to trap all exceptions, just use catch without arguments:
catch
{
Write-Output "Directory Exists Already"
}
if you want to trap a specific exception, first find out which one it is, by checking the value of
$error[0].Exception.GetType().FullName
and in your case the value is:
System.IO.IOException
then you can use this value as an argument to your catch, like this:
catch [System.IO.IOException]
{
Write-Output "Directory Exists Already"
}
Source worth reading: An introduction to Error Handling in Powershell

Answer 2

In addition you can spot exactly Directory Exist (unfortunally no File Exist error type for files).
$resExistErr=[System.Management.Automation.ErrorCategory]::ResourceExists
try {
New-Item item -ItemType Directory -ErrorAction Stop
}
catch [System.IO.IOException]
{
if ($_.CategoryInfo.Category -eq $resExistErr) {Write-host "Dir Exist"}
}

Answer 3

If you add -ErrorAction Stop to the line creating the directory you can catch [System.IO.IOException](not [System.IO]). You should also catch all other exceptions that can potentially occur:
try {
New-Item -Path $copyDrive\$folderDate -ItemType directory -ErrorAction Stop
Copy-Item $parentDirectory\$userDirectory\$folderName\* $copyDrive\$folderDate -ErrorAction Stop
}
catch [System.IO.IOException] {
WriteOutput $_.Exception.Message
}
catch {
#some other error
}

Answer 4

I don't suggest actually catching the error in this case. Although that may be the correct action in general, in this specific case I would do the following:
$newFolder = "$copyDrive\$folderDate"
if (-not (Test-Path $newFolder)) {
New-Item -Path $newFolder -ItemType directory
Copy-Item $parentDirectory\$userDirectory\$folderName\* $newFolder
} else {
Write-Output "Directory Exists Already"
}