Problem with switch statement in a while loop in PowerShell - powershell

Question

For whatever reason the While loop works by itself, the Switch statement works by itself, when I combine them.. the While loop works ok, the Switch statement though.. not so much.
y or n are only values the While loop accepts, the problem is that when I give it y or n, none of the code gets executed, the script just finishes.
PowerShell version is 5.1.
While (($UserInput = Read-Host -Prompt "Are you sure? (y/n)") -notmatch '^n$|^y$') {
Switch ($UserInput) {
'y' {
Try {
Write-Output "Success."
}
Catch {
Write-Output "Error."
}
}
'n' {
Write-Output "Cancelled."
}
}
}

Answer 1

here's a rather more robust method to do what you seem to want. it sets up the valid choices, asks for input, detects invalid input, warns about that, displays the "success" or "failure" messages - all without twisty logic. [grin]
$Choice = ''
$ValidChoiceList = #(
'n'
'y'
)
while ([string]::IsNullOrEmpty($Choice))
{
$Choice = Read-Host 'Are you sure? [n/y] '
if ($Choice -notin $ValidChoiceList)
{
[console]::Beep(1000, 300)
Write-Warning ('Your choice [ {0} ] is not valid.' -f $Choice)
Write-Warning ' Please try again & choose "n" or "y".'
$Choice = ''
pause
}
switch ($Choice)
{
'y' {Write-Host 'Success!'; break}
'n' {Write-Warning ' Failure!'; break}
}
}
on screen output ...
Are you sure? [n/y] : t
WARNING: Your choice [ t ] is not valid.
WARNING: Please try again & choose "n" or "y".
Press Enter to continue...:
Are you sure? [n/y] : y
Success!

Answer 2

You are using -notmatch. Hence While loop is resulting in false and loop is not getting executed. As you want to execute the script until you get 'y' or 'n' as input, just use ! which will execute the script until it receives 'y' or 'n' as input.
Use below code:
While (!($UserInput = Read-Host -Prompt "Are you sure? (y/n)") -notmatch '^n$|^y$') {
Switch ($UserInput) {
'y' {
Try {
Write-Output "Success."
}
Catch {
Write-Output "Error."
}
}
'n' {
Write-Output "Cancelled."
}
}
}