Try/Catch Example - powershell

Question

I understand Stackoverflow isn't a write your code for you forum, absolutely, but I'm finding it very difficult to find a good example of try/catch proper usage in Powershell. I have read up on fundamentals, and understand the theoretical concept, but execution I'm struggling with.
Here is a simple script that queries Active Directory:
do {
clear
Import-Module active*
"============ WhoIs Lookup ============="
Write-Host ""
$who = Read-Host "WhoIs";
$req = Get-ADUser -Identity $who
Write-Host ''
Write-Host "$who is " -NoNewline
Write-Host $req.Name -ForegroundColor Cyan
pause
} while ($run =1)
An example error is:
Get-ADUser : Cannot find an object with
identity: '5621521' under: 'DC=dcsg,DC=com'.
At C:\Tools\CSOCTools\Who_Is\whoIs.ps1:10
char:12
+ $req = Get-ADUser -Identity $who
+ ~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ObjectNotFoun
d: (5621521:ADUser) [Get-ADUser], ADIde
ntityNotFoundException
+ FullyQualifiedErrorId : ActiveDirecto
ryCmdlet:Microsoft.ActiveDirectory.Mana
gement.ADIdentityNotFoundException,Micr
osoft.ActiveDirectory.Management.Comman
ds.GetADUser
How would I catch this User Not Found error?

Answer 1

Simple example:
try {
Get-ADUser -Identity “bleh”
}
catch [Microsoft.ActiveDirectory.Management.ADIdentityNotFoundException]
{
Write-Warning “AD computer object not found”
}
For your case:
do {
clear
Import-Module active*
"============ WhoIs Lookup ============="
Write-Host ""
$who = Read-Host "WhoIs";
try {
$req = Get-ADUser -Identity $who
}
catch [Microsoft.ActiveDirectory.Management.ADIdentityNotFoundException]
{
Write-Warning “AD user object not found”
Write-Host ''
Write-Host "$who is " -NoNewline
Write-Host $req.Name -ForegroundColor Cyan
}
pause
} while ($run =1)
Edit: I put the Write-Host into the catch as you're eventually trying to reference to NULL when there's no object.

Answer 2

I got a very good example from here. For the exception types after the Catch (where I have two of them) I just grabbed them straight from the error message you provided. I haven't tried this out many times in my experience, let me know if it works for ya!
Try
{
do {
clear
Import-Module active*
"============ WhoIs Lookup ============="
Write-Host ""
$who = Read-Host "WhoIs";
$req = Get-ADUser -Identity $who
Write-Host ''
Write-Host "$who is " -NoNewline
Write-Host $req.Name -ForegroundColor Cyan
pause
} while ($run =1)
}
Catch [Microsoft.ActiveDirectory.Management.ADIdentityNotFoundException],[Microsoft.ActiveDirectory.Management.Commands.GetADUser]
{
# Error message here
}