PowerShell: Referencing a property with spaces

Question

I am trying to create a script that will check a registry key/value. If the value is a certain version, write an output. If the value is not that version, then create a new value. The problem I am coming across is the property is split into two words.

The key is hklm:software\dg

The value name is "Agent version"

The value data is 7.8.5.005

I have tried the script below but I'm just not familiar with how to properly check the version of the value "Agent version" since it is split into two words. The script always creates the new test value. I have tried double quotes, single quotes, curly brackets around agent version. Nothing seems to work. If there is an easier way to do this, I am all ears. Thanks in advance!

$val = Get-ItemProperty -Path hklm:software\dg

if($val.'agent version' -eq 7.8.5.005) {
Write-Host Agent is current -ForegroundColor Green
}
else {
New-ItemProperty -Path hklm:software\dg -Name "Test" -value 0
}

Answer 1

Building on the great comments on the question:

tl;dr

Replace $val.'agent version' -eq 7.8.5.005 with:

# Note the [version] cast, and the '...' around the RHS operand.
# Because the LHS uses [version], it isn't also needed before '7.8.5.5'
[version] $val.'agent version' -eq '7.8.5.5'  # Note: 0-padding is irrelevant

In general, to construct a literal [version] instance, you must cast from a string:

[version] '7.8.5.5' # '...' required

---

To address the general question implied by your post's title:

• Enclosing a (literal) property name containing special characters such as spaces in '...' is indeed the right solution (in the unlikely event that the name itself contains ' instances, double them ('')).

  • As for which characters PowerShell considers special in a property name (identifier), see this answer.

---

As for what you tried:

• The Windows registry has no data type that directly represents a version number - a string value (REG_SZ) is used to represent version numbers, and that translates into a .NET [string] instance via Get-ItemProperty or - to retrieve a registry value directly - via Get-ItemPropertyValue.

• Similarly, PowerShell also has no literal notation for version numbers, but you can cast a string to [version] in order to construct a System.Version instance.

  • As zett42 notes, the unquoted 7.8.5.005 literal effectively evaluates to $null, because it is parsed as [double] instance 7.8 on which you're trying to access the (implicitly stringified) [double] instance 5.005 as a property, which obviously doesn't exist.

  • You can gain insights into how PowerShell parses such expressions by enclosing them in a script block ({ ... }), and drilling down into that script block's .Ast property - note how 5.005 is listed as a Member access:

    PS> { 7.8.5.005 }.Ast.EndBlock.Statements.PipelineElements.Expression
    
    Expression      : 7.8
    Member          : 5.005
    Static          : False
    NullConditional : False
    StaticType      : System.Object
    Extent          : 7.8.5.005
    Parent          : 7.8.5.005
    

Only [version] instances compare meaningfully as version numbers.

Since it is sufficient for the LHS of a comparison operation, such as with -eq, to be of type [version] in order to compare version numbers, you can take a shortcut and use a string literal as the RHS, as shown at the top.