Powershell Input validation for integer

Question

I wanted to write a script that prompts the user to enter a time in minutes for to start shutdown timer. I got it to work but had no input validation. This is what I have.

DO{
try{

$numOk= $true
[int] $minutes= Read-Host "Enter the amount in minutes until a shut down (0 to cancel)"
#$minutes= [int]$minutes

}
catch{

#if($minutes -isnot [int]){}
$numOk= $false
Write-Host "Input is not an integer!!!!!"
}

} while ($numOk = $false)


[int] $seconds= $minutes*60

if($seconds -eq 0){
shutdown -a
}
else{
shutdown -s -t $seconds
}

I am getting a very weird value when I type a letter in.

PS C:\Users\USER\Desktop\shut down> .\shutdownTimer.ps1
Enter the amount in minutes until a shut down (0 to cancel): a
Input is not an integer!!!!!
Cannot convert value "555555555555555555555555555555555555555555555555555555555555" to type "System.Int32". Error: "Value was either 
too large or too small for an Int32."
At C:\Users\USER\Desktop\shut down\shutdownTimer.ps1:25 char:1
+ [int] $seconds= $minutes*60
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvalidCastFromStringToInteger

shutdown : Unable to abort the system shutdown because no shutdown was in progress.(1116)
At C:\Users\USER\Desktop\shut down\shutdownTimer.ps1:29 char:1
+ shutdown -a
+ ~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (Unable to abort...progress.(1116):String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError

Not quite sure where all those fives come from.

veefu · Accepted Answer · 2018-08-12 06:03:13Z

9

Your code has an error at while ($numOk = $false). In powershell, = is the assignment operator. The comparison operators are shell-style: -eq, -ne, -gt, -gte, -lt, -lte, -like etc. See here

You may want to use [int]::TryParse to test the input, something like this:

$inputValue = 0
do {
    $inputValid = [int]::TryParse((Read-Host 'gimme a number'), [ref]$inputValue)
    if (-not $inputValid) {
        Write-Host "your input was not an integer..."
    }
} while (-not $inputValid)

answered Aug 12, 2018 at 6:03

veefu

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1 Comment

Thy Process Over a year ago

Simply changing that line to -eq allowed for the loop to properly work. If I enter in a letter now, my Write-Host statement shows up and asks for the user to enter input again. Thanks!

vrdse · Accepted Answer · 2018-08-12 07:54:42Z

2

If you typecast a variable as int, PowerShell automatically checks the input. a cannot be assigned to $minutes as it cannot be converted to int. I'm sure your variable was already assigned in your PowerShell session with a as string. 'a' * '60' is 60 times a which produces your error. Cleanup your variables and better yet rewrite your code. There is no need for Read-Host and all the input validation. PowerShell does all that for you.

param(
    # Enter the amount in minutes until a shut down
    [int]$Minutes = 1
)
$Seconds = $Minutes * 60
Start-Sleep -Seconds $Seconds
Stop-Computer

answered Aug 12, 2018 at 7:54

vrdse

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