if with -ne and -or operators not working in powershell

Question

The following if statements with -ne and -or operators is not working (Note I did not include the braces). $MyVariable is an integer coming in from a parameter in a function and having the if statement check the value. What I want is if $MyVariable is not equal to 16, 24 or 32 then return with error message otherwise continue. Calling the function as FunctionName 16; in the ps1 script.

Function is defined as follows:

function FunctionName
{
  param([Parameter(Mandatory = $false, Position = 0)]
            [AllowNull()]
            [int]   $MyVariable,
            [Parameter(Mandatory = $false, Position = 1)]
            [bool] $MyVariable2,
            [Parameter(Mandatory = $false, Position = 2)]
            [bool] $MyVariable3);
  if (...
}

What am I doing wrong in the following if statements?

if ($MyVariable -ne 16 -or $MyVariable -ne 24 -or $MyVariable -ne 32)...
if (16 -ne $MyVariable -or 24 -ne $MyVariable -or 32 -ne $MyVariable)...
if (($MyVariable -ne 16) -or ($MyVariable -ne 24) -or ($MyVariable -ne 32))...

Logic flaw. At least two of the -ne comparisons will always be true. Use -and instead, or -eq for the comparison — Mathias R. Jessen
– Mathias R. Jessen, Commented Dec 29, 2016 at 16:39
Yes. After re-looking at the logic it makes sense. Thank you. — Costa Zachariou
– Costa Zachariou, Commented Dec 29, 2016 at 16:48

Mathias R. Jessen · Accepted Answer · 2016-12-29 16:49:13Z

3

If any one of the three equality comparisons return $false, the two others must return true (if $x equals 16 it will never equal 24 or 32), and so the statement will always evaluate to $true.

Change -or to -and to test for all 3 cases:

if ($MyVariable -ne 16 -and $MyVariable -ne 24 -and $MyVariable -ne 32){}

or check whether it is equal rather than not:

if ($MyVariable -eq 16 -or $MyVariable -eq 24 -or $MyVariable -eq 32){}

or, use the -contains operator instead:

if (@(16,24,32) -contains $MyVariable){}

answered Dec 29, 2016 at 16:49

Mathias R. Jessen

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