Making PowerShell expressions easier

Expressions in PowerShell have a weird syntax and can quickly become complicated and hard to read. I thought about a way to make the syntax a bit easier to read and came up with a solution that might work for some cases. This solution contains two classes which can be used when piping to Select-Object for example. The first class describes the actual expression.

class Xpression
{
    [string]$Name
    [scriptblock]$Expression
    [hashtable] getExpression() { 
        return @{ Name = $this.Name; Expression = $this.Expression }
    }
}

The second class is an array of the first class. This class also have overloaded methods for adding expressions or property names. The Get() method returns all expressions and properties (converted to expressions).

class XpressionArray
{
    [Xpression[]]$Expression
    [array] Get() { 
        return $this.Expression.getExpression()
    }
    Add([string]$n, [scriptblock]$x) { 
        $temp = New-Object -TypeName Xpression
        $temp.Name = $n
        $temp.Expression = $x
        $this.Expression += $temp
    }
    Add([string]$n) { 
        $temp = New-Object -TypeName Xpression
        $temp.Name = $n
        $temp.Expression = [Scriptblock]::Create('$_.' + $n ) 
        $this.Expression += $temp
         
    }
}

So how can we use this? Its quite easy actually. First create an object with TypeName “XpressionArray”.

$exp = New-Object -TypeName XpressionArray

Then add the properties or expressions you need using the Add() method.

$exp.Add('Name')
$exp.Add('Id')
$exp.Add('KB',{ $_.WorkingSet / 1Kb })
$exp.Add('MB',{ $_.WorkingSet / 1Mb })

Now lets see if this works. Run the following command to use the method Get() in the pipeline.

Get-Process -Name powershell* | select $exp.Get() | Format-Table
Get-Process -Name powershell* | select $exp.Get() | Get-Member

And it works! These classes can make the code look a bit more clean in some cases so try it for yourself to see if it fits your scenarios.

- Written by John Roos on July 14, 2015