-or Returning a false positive ??

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This topic contains 6 replies, has 4 voices, and was last updated by

 
Participant
4 years, 3 months ago.

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  • #18010

    Participant
    Points: 1
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    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

  • #18011

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

    Should give you what you expect.

  • #18014

    Participant
    Points: 305
    Helping Hand
    Rank: Contributor

    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}

  • #18016

    Member
    Points: 0
    Rank: Member

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

    • $foo -Contains 'X'
    • 'Z'

    $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.

  • #18019

    Participant
    Points: 305
    Helping Hand
    Rank: Contributor

    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...

  • #18023

    Participant
    Points: 0
    Rank: Member

    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.

  • #18028

    Participant
    Points: 1
    Rank: Member

    Thanks guys

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