Powershell, check for blank input, zero evaluates as blank/null - powershell

Question

I am trying to validate a simple powershell input. I want to allow the number zero as valid input, but blank (just pressing enter) is not valid input. I am having the most difficult time with the validation. Everything works EXCEPT when the user enters the number zero.
I have tried checking the length, checking for null, etc.
Consider the code below.
If you enter 0 (zero) the output is the same as if you just press [enter] (no input)
Pick a number 0-6: 0
You picked 0
blank input
equals zero
too short
$OUchoice = -1
do
{
try{
$OUchoice = Read-Host "Pick a number 0-6"
}
catch{
write-host "invalid input"
}
Write-Host "You picked $OUchoice"
if ($OUchoice -gt 6) {write-host "too high"}
if ($OUchoice -lt 0) {write-host "too low"}
if ($OUchoice -eq "") {write-host "blank input"}
if ($OUchoice -eq 0 ) {write-host "equals zero"}
if ($OUchoice -eq $null ) {write-host "Null"}
if (!($OUchoice)) {write-host "too short"}
}
until (($OUchoice -ge 0) `
-and ($OUchoice -le 6) `
-and (($ouchoice)))
write-host "OK"
I have tried -eq $NULL and -eq "". What is the proper way to allow zero and disallow blank input?

Answer 1

Problem lies in this:
PS> 0 -eq ""
True
When two values of different type are compared second argument is casted to the type of the first. Unfortunately for you:
PS> [int]""
0
empty string when casted to int produces 0. In your case fix is easy: just reverse the order of operands as 0 casted to string would end up being '0':
if ("" -eq $OUchoice) {write-host "blank input"}

Answer 2

This is what I came up with. I ensure that the $OUChoice is an Int when you compare it against other numbers. This ensures that null input is a 0 and also allows for negative values.
$OUchoice = -1
do
{
try{
$OUchoice = Read-Host "Pick a number 0-6"
}
catch{
write-host "invalid input"
}
Write-Host "You picked $OUchoice"
Switch ($OUchoice) {
{
[string]::IsNullOrEmpty($OUchoice)} {
write-host "Null Input"
Break
}
{
[int]$OUchoice -gt 6} {
write-host "too high"
Break
}
{
[int]$OUchoice -lt 0} {
write-host "too low"
Break
}
{
[int]$OUchoice -eq 0 } {
write-host "equals zero"
Break
}
}
}
until (([int]$OUchoice -ge 0) -and ([int]$OUchoice -le 6) -AND (-NOT [string]::IsNullOrEmpty($OUchoice)))
write-host "OK"

Answer 3

Nest your ifs (I didn't test much, but did check the zero and blank cases):
if (-not ($OUchoice -eq ""))
{
if ($OUchoice -gt 6) {write-host "too high"}
if ($OUchoice -lt 0) {write-host "too low"}
if ($OUchoice -eq 0 ) {write-host "equals zero"}
if ($OUchoice -eq $null ) {write-host "Null"}
if (!($OUchoice)) {write-host "too short"}
}
else
{
Write-Output "blank input"
}
Output:
PS C:\users\mattp_000> .\x.ps1
Pick a number 0-6:
You picked
blank input
Pick a number 0-6: 0
You picked 0
equals zero
OK
PS C:\users\mattp_000> .\x.ps1
Pick a number 0-6: 3
You picked 3
OK
PS C:\users\mattp_000>