Using Read-host with Input validation and TRAP - powershell

Question

I'm just a typical admin trying to make a simple script for some IT assistants in remote offices, to make domain joins easier while minimizing potential errors. The script's end game is to run the one-liner command Add-Computer -DomainName $DomainToJoin -OUPath $LocDN -NewName $WS_NewName -Restart.
But the whole script is supposed to include input validation for the computer's new name as well as for the target OU for the two-letter code for the remote office.
Googling for code snippets for days, esp. from sites like yours, was very helpful. But the problem I have now is I couldn't find the right codes to combine Read-Host , input length validation, and TRAP to work together without losing the value for my variables.
Pardon my coding as obviously I'm no real PS scripter, and I know the wrong portions of it are very basic. I would want to spend more time if I had the luxury, but I would really so much appreciate it if you could point me in the right direction.
Thank you so much in advance.
Please see my code below:
# START: Display name and purpose of invoked script
$path = $MyInvocation.MyCommand.Definition
Clear-Host
Write-Host $path
Write-Host " "
Write-Host "This script will allow you to do the following in a single-step process:"
Write-Host "(1) RENAME this computer"
Write-Host "(2) JOIN it to MYDOMAIN"
Write-Host "(3) MOVE it to a target OU"
Write-Host "(4) REBOOT"
Write-Host " "
Pause
# Function: PAUSE
Function Pause ($Message = "Press any key to continue . . . ") {
if ((Test-Path variable:psISE) -and $psISE) {
$Shell = New-Object -ComObject "WScript.Shell"
$Button = $Shell.Popup("Click OK to continue.", 0, "Script Paused", 0)
}
else {
Write-Host -NoNewline $Message
[void][System.Console]::ReadKey($true)
Write-Host
}
Write-Host " "
}
# Function: Define the parameters
Function Define-Parameters {
# Specify new computer name, with validation and TRAP
$WS_NewName = $null
while ($null -eq $WS_NewName) {
[ValidateLength(8,15)]$WS_NewName = [string](Read-Host -Prompt "NEW NAME of computer (8-15 chars.)" )
TRAP {"" ;continue}
}
Write-Host " "
# Domain to join.
$DomainToJoin = 'mydomain.net'
# Specify the target OU, with validation and trap
$baseOU='OU=Offices OU,DC=mydomain,DC=net'
$OU2 = $null
while ($null -eq $OU2) {
[ValidateLength(2,2)]$OU2 = [string](Read-Host -Prompt 'Target OU (TWO-LETTER code for your office)' )
TRAP {"" ;continue}
}
Write-Host " "
$LocDN = "OU=$OU2,$baseOU"
}
# Function: Summary and confirmation screen for defined parameters.
Function Confirm-Parameters {
Write-Host "==========================================================================="
Write-Host "Please confirm that you are joining this computer to
$DomainToJoin (MYDOMAIN)"
Write-Host "with the following parameters:"
Write-Host ""
Write-Host ""
Write-Host "Computer's NEW NAME: $WS_NewName"
# Write-Host "Domain to Join: $DomainToJoin"
Write-Host "TARGET mission OU: $OU2"
}
# Call Define-Parameters Function
Define-Parameters
# Call Confirm-Parameters Function
Confirm-Parameters
<#
Some more code here
#>
# FINAL COMMAND if all else works: Join the computer to the domain, rename it, and restart it.
# Add-Computer -DomainName $DomainToJoin -OUPath $LocDN -NewName $WS_NewName -Restart

Answer 1

In your code, you have a lot of things defined very strangely. Your functions create a new scope and the variables you're trying to define therein will disappear after calling them unless you change the variable scope (in this case, to $script: or $global:). Also, to use functions, you need to define them first (your Pause doesn't actually do anything)
Here's something you can do with your Define-Parameters function (I suggest looking at Get-Verb)
# Domain to join.
$DomainToJoin = 'mydomain.net'
# Function: Define the parameters
Function Get-Parameters {
do {
$global:WS_NewName = Read-Host -Prompt 'NEW NAME of computer (8-15 chars)'
} until ($WS_NewName.Length -gt 7 -and $WS_NewName.Length -lt 16)
''
do {
$global:OU2 = Read-Host -Prompt 'Target OU (TWO-LETTER code for your office)'
} until ($OU2 -match '^[a-z]{2}$')
''
$OU2 = "OU=$global:OU2,OU=Offices OU,DC=mydomain,DC=net"
}
I'd strongly recommend moving away from the ISE to do your testing and test in an actual powershell console.

Answer 2

Perhaps Try/Catch block instead of trap?
Try {
[ValidatePattern('^\w{8,15}$')]$compname=read-host 'enter comp name' -ErrorAction Stop
[ValidatePattern('^\w{2}$')]$OU=read-host 'enter OU name' -ErrorAction Stop
}
Catch {
$ErrorMessage = $_.Exception.Message
$ErrorLineNumber = $_.InvocationInfo.ScriptLineNumber
$ErrorCommandName = $_.InvocationInfo.InvocationName
Write-Error -Message "The error message was: <$ErrorMessage>, script line: <$ErrorLineNumber>, command name: <$ErrorCommandName>"
exit 255
}