CODEWITHSUNDEEP
powershellnullactive-directoryswitch-statement
jimbo.19
jimbo.19

Reputation: 23

PowerShell Switch Statement Issue

I have the following simple code and it isn't working (simplified from a much larger function)

What am I missing?

Snippet 1:

$user = "no.one"
$myADUsr = Get-ADObject -Filter { sAMAccountName -like $user }

switch ($myADUsr) {

    $null { 'User object variable is null' }
    default  { 'User object variable has a value' }

}

Snippet 2:

$myADUsr = $null

switch ($myADUsr) {

    $null { 'The variable is null' }
    default { 'The variable has a value' }

}

Snippet 3:

clear-host
$member = "no.one"
$adobject = Get-ADObject -Filter { sAMAccountName -like $member }


'=== Frist switch ==='
switch ($adobject) {
    {$null} { "tests as null"}
    {$null -eq $_ } { 'another null test' }
    {[string]::IsNullOrEmpty($_)} {'string null test'}
    {$_ -eq [string]::Empty} { 'another string null test'}
    {$null -ne $_ } { 'not null' }
    default { "I don't think this is working ..." }
}



'==== if ====='
If ($null -eq $adobject) { 'null' } else { 'not null' }



'==== second switch ==='
$nullvariable = $null
switch ($nullvariable) {
    $adobject { 'null object' }
    $null { "null"}
    default { "not null" }
}

Upvotes: 2

Views: 1190

Answers (2)

jimbo.19
jimbo.19

Reputation: 23

It think updating my original snippet #1 like this gets me out of trouble, it seems to work so I can continue to use the switch statement I have already written. I'm still testing. 

$user = "no.one"
$myADUsr = Get-ADObject -Filter "sAMAccountName -like '$user'"

if ( @($myADUsr).Count -eq 0 ) { $myADUsr = $null }

switch ($myADUsr) { 
    $null { 'User object variable is null' }
    default { 'User object variable has a value' }
}

Upvotes: 0

mklement0
mklement0

Reputation: 440142

  • The switch statement implicitly operates on collections (enumerable data types), and evaluates its branches for each element of the enumeration.

  • A function or cmdlet call that yields no output technically outputs the [System.Management.Automation.Internal.AutomationNull]::Value singleton, which can be conceived of as an array-valued $null - that is, in enumeration contexts such as switch it behaves like an empty collection: there's nothing to enumerate.

Therefore, because $myADUsr in your example contains [System.Management.Automation.Internal.AutomationNull]::Value due to Get-AdUser not producing any output, the switch statement is effectively skipped.

If all you need to know is whether an AD user object was returned, use PowerShell's implicit to-Boolean conversion in an if statement, because in an expression context [System.Management.Automation.Internal.AutomationNull]::Value behaves like $null (and therefore evaluates to $false):

$myADUsr = Get-ADObject -Filter 'sAMAccountName -like $user'

if ($myAdUsr) {
  'User object variable has a value'
}
else {
  'User object variable is null' 
}

Upvotes: 3

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