Tied Variables in PowerShell
With Add-Type and $executioncontext you can add special varibles that have tied values.
I made $random, and $now
add-type @"
using System;
using System.Management.Automation;
public class RandomVariable : PSVariable
{
Random r;
public RandomVariable ()
: base("Random", 0, ScopedItemOptions.ReadOnly | ScopedItemOptions.AllScope)
{r = new Random();}
public override object Value
{
get
{
return r.Next();
}
}
}
"@
$executioncontext.SessionState.PSVariable.Set((new-object RandomVariable))
add-type @"
using System;
using System.Management.Automation;
public class NowVariable : PSVariable
{
public NowVariable ()
: base("Now", 0, ScopedItemOptions.ReadOnly | ScopedItemOptions.AllScope)
{}
public override object Value
{
get
{
return DateTime.Now;
}
}
}
"@
$executioncontext.SessionState.PSVariable.Set((new-object NowVariable))
Results is,
PS C:\tmp> $Random
229309908
PS C:\tmp> $Random
1759972224
PS C:\tmp> $Now
Thursday, 26 March 2009 3:20:29 PM
I got this from Lee, where you can bind the behaviour to ScriptBlocks instead of C#, making it even easier to use. See attached
It has in it,
get
{
if(getter != null) { return getter.Invoke(); }
else { return null; }
}
Which is a simple way to cross over to PowerShell from C#
And you can use it like so,
PS C:\temp> New-ScriptVariable.ps1 GLOBAL:today { (Get-Date).DayOfWeek }
PS C:\temp> $today
Wednesday
Cheers,
Ibrahim Abdul Rahim [MSFT]
