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PowerShell: The automatic variable $NULL

$null is an automatic variable. It is the only instance of the null type.

$null is also referred to as null value.

The value of a PowerShell variable that was not assigned a value (yet) is $null. The value of $null itself is the C# value null.

$null can be assigned any value; yet, the value of $null remains unchanged:

PS C:\> $null = mkdir temp-dir
PS C:\> $null

Assigning a value of an expression to $null is typically used to hide the returned result on the console. In order to be more explicit about this intention, some prefer to write mkdir temp-dir | out-null instead.

$null has a count property whose value is 0:

PS C:\> $null.count
0

Types that can't be null

Strings cannot be $null even though $null can be assigned to them.

PS C:\> [string] $txt = $null
PS C:\> $txt -eq $null
False

A string that was assigned $null is the empty string:

PS C:\> $txt -eq ''
True

Integers cannot be $null as well and become 0 if a $null is assigned to them:

PS C:\> [int] $i = $null
PS C:\> $i -eq $null
False
PS C:\> $i
0

Checking for a null value

Unlike the null value in SQL, $null can be compared to itself. Thus, comparison operators such as -eq can be used to check if a variable is $null:

if ($val -eq $null) {
  'val is null'
} else {
  'val is not null'
}

PowerShell: The automatic variable $NULL

Types that can't be null

Checking for a null value

See also