-or Returning a false positive ??

PowerShell Help
1

Hi Guys,

Can someone tell me why I get $TRUE with this?

$foo = @('A','B','C')

if ($foo -Contains 'X') {Write-Output $foo}


if ($foo -Contains 'X' -or 'Z') {Write-Output $foo}
A
B
C

Thanks

2 
if (($foo -Contains 'X') -or ($foo -Contains 'Z')) {Write-Output $foo}

Should give you what you expect.

3

If you read about_Operators, -or is a Logical operator used to ‘to connect conditional statements into a single complex conditional.’ Comparison operators such as -contains, -like, -eq … are doing variable comparisons.

if (($foo -Contains ‘X’) -or ($foo -contains ‘Z’)) {Write-Output $foo}
if (($foo -Contains ‘X’) -and ($foo -contains ‘Z’)) {Write-Output $foo}

4

To clarify further, this expression: ($foo -Contains ‘X’ -or ‘Z’) is a compound of the following two expressions:

[ul]
[li]$foo -Contains ‘X’[/li]
[li]‘Z’[/li]
[/ul]

$foo -Contains ‘X’ is obviously false. The expression ‘Z’, however, is a string, not a boolean. When strings are cast to booleans (which is what PowerShell is doing here), they’re False if they are null or empty, and True if they contain any characters. As you can see if you run this:

[bool]'Z'

The second part of your original compound expression is always true.

5

It’s interesting that Z returns true if it’s casting it as boolean. Boolean is typically translated to a 0 or 1 to indicate a false or true. A bit misleading…

6

Boolean is always through of as just 0 and 1, it’s more accurately Zero and Non-Zero with 0 being False, and everything else being true. Although this varies from language to language on how it gets used.

7

Thanks guys