Powershell Only Add to Array if it doesn't exist

To fix your code, try -notcontains or at least WRAP your contains-test in parantheses. Atm. your test reads:

If "NOT array"(if array doens't exist) contains word.

This makes no sense. What you want is:

If array does not contain word..

That's written like this:

If (-not ($IncorrectArray -contains $Word))

-notcontains is even better, as @dugas suggested.

The first time around, you evaluate -not against an empty array, which returns true, which evaluates to: ($true -contains 'AnyNonEmptyString') which is true, so it adds to the array. The second time around, you evaluate -not against a non-empty array, which returns false, which evaluates to: ($false -contains 'AnyNonEmptyString') which is false, so it doesn't add to the array.

Try breaking your conditions down to see the problem:

$IncorrectArray = @()$x = (-not $IncorrectArray) # Returns trueWrite-Host "X is $x"$x -contains 'hello' # Returns true

then add an element to the array:

$IncorrectArray += 'hello'$x = (-not $IncorrectArray) # Returns false    Write-Host "X is $x"$x -contains 'hello' # Returns false

See the problem? Your current syntax does not express the logic you desire.

You can use the notcontains operator:

Clear-Host$Words = @('Hello', 'World', 'Hello')# This will work$IncorrectArray = @()ForEach ($Word in $Words){  If ($IncorrectArray -notcontains $Word)  {    $IncorrectArray += $Word  }}