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Filter Expression

The original purpose of the Filter Component is to allow flexible filter logic in data that is not supposed to be executable code. And the Filter Expression is the part that brings it all together.

It allows the user to type almost plain PowerShell filter code, without granting them direct code execution.

Example Filter Expression:

IsBeer -and (InBar -or InCellar -or InFridge)

Legal Content​

So what everything can you put into a Filter Expression?

  • The name of the Conditions
  • Any logical operator (-and, -or, -xor, -not)
  • Parenthesis ( (...) )

Executing an Expression​

So, let's test this thing:

$expression = 'IsBeer -and (InBar -or InCellar -or InFridge)'
Invoke-PSFFilter -Expression $expression -SetModule Bartender -SetName Bar -ArgumentList $beverage

Which will return $true if the condition applies or $false if not so.

Builtin Demo

The PSFramework comes with a builtin Condition Set: Environment:

Invoke-PSFFilter -SetModule PSFramework -SetName Environment -Expression 'OSWindows -and PS7Plus'

The Filter object​

For repeated validations, it might be more efficient to have an object at hand, rather than keep calling the function again and again. This can be done with the New-PSFFilter command:

$filter = New-PSFFilter -SetModule Bartender -SetName Bar -Expression 'IsBeer -and (InBar -or InCellar -or InFridge)'
$filter.Evaluate($beverage)

Validating an Expression​

We can validate an expression before executing it, by using the Test-PSFFilter command:

Test-PSFFilter -SetModule PSFramework -SetName Environment -Expression 'IsWindows -and PS7Plus -and Elevated'
warning

This can easily be confused with the result of Invoke-PSFFilter! The truth return of Test-PSFFilter is whether the expression is valid, not whether any objects being tested are valid against the expression!