¿Cómo asigno un valor nulo a una variable en PowerShell?

scripting null

Question

Quiero asignar un valor nulo a una variable llamada $dec , pero me da errores. Aquí está mi código:

import-module activedirectory
$domain = "domain.example.com"
$dec = null
Get-ADComputer -Filter {Description -eq $dec}

Answer 1

Estas son variables automáticas, como $null , $true , $false etc.

about_Automatic_Variables , consulte https://technet.microsoft.com/en-us/library/hh847768.aspx?f=255&MSPPError=-2147217396

$NULL
$null is an automatic variable that contains a NULL or empty value. You
can use this variable to represent an absent or undefined value in commands
and scripts.
Windows PowerShell treats $null as an object with a value, that is, as an
explicit placeholder, so you can use $null to represent an empty value in a
series of values.
For example, when $null is included in a collection, it is counted as one of
the objects.
C:/PS> $a = ".dir", $null, ".pdf"
C:/PS> $a.count
3
If you pipe the $null variable to the ForEach-Object cmdlet, it generates a
value for $null, just as it does for the other objects.
PS C:/ps-test> ".dir", "$null, ".pdf" | Foreach {"Hello"}
Hello
Hello
Hello
As a result, you cannot use $null to mean "no parameter value." A parameter
value of $null overrides the default parameter value.
However, because Windows PowerShell treats the $null variable as a placeholder,
you can use it scripts like the following one, which would not work if $null
were ignored.
$calendar = @($null, $null, “Meeting”, $null, $null, “Team Lunch”, $null)
$days = Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"
$currentDay = 0
foreach($day in $calendar)
{
if($day –ne $null)
{
"Appointment on $($days[$currentDay]): $day"
}
$currentDay++
}
Appointment on Tuesday: Meeting
Appointment on Friday: Team lunch

Answer 2

Si el objetivo es simplemente listar todos los objetos de la computadora con un atributo de descripción vacío, intente esto

import-module activedirectory
$domain = "domain.example.com"
Get-ADComputer -Filter ''*'' -Properties Description | where { $_.Description -eq $null }

Answer 3

Usa $dec = $null

De la documentation :

$ null es una variable automática que contiene un valor NULL o vacío. Puede usar esta variable para representar un valor ausente o indefinido en comandos y scripts.

PowerShell trata $ null como un objeto con un valor, es decir, como un marcador de posición explícito, por lo que puede usar $ null para representar un valor vacío en una serie de valores.