Invoking powershell cmdlets from C#

Question

I'm trying to learn how to call PS cmdlets from C#, and have come across the PowerShell class. It works fine for basic use, but now I wanted to execute this PS command:

Get-ChildItem | where {$_.Length -gt 1000000}

I tried building this through the powershell class, but I can't seem to do this. This is my code so far:

PowerShell ps = PowerShell.Create();
ps.AddCommand("Get-ChildItem");
ps.AddCommand("where-object");
ps.AddParameter("Length");
ps.AddParameter("-gt");
ps.AddParameter("10000");


// Call the PowerShell.Invoke() method to run the 
// commands of the pipeline.
foreach (PSObject result in ps.Invoke())
{
    Console.WriteLine(
        "{0,-24}{1}",
        result.Members["Length"].Value,
        result.Members["Name"].Value);
} // End foreach.

I always get an exception when I run this. Is it possible to run the Where-Object cmdlet like this?

Answer 1

Length, -gt and 10000 are not parameters to Where-Object. There is only one parameter, FilterScript at position 0, with a value of type ScriptBlock which contains an expression.

PowerShell ps = PowerShell.Create();
ps.AddCommand("Get-ChildItem");
ps.AddCommand("where-object");
ScriptBlock filter = ScriptBlock.Create("$_.Length -gt 10000")
ps.AddParameter("FilterScript", filter)

If you have more complex statements that you need to decompose, consider using the tokenizer (available in v2 or later) to understand the structure better:

    # use single quotes to allow $_ inside string
PS> $script = 'Get-ChildItem | where-object -filter {$_.Length -gt 1000000 }'
PS> $parser = [System.Management.Automation.PSParser]
PS> $parser::Tokenize($script, [ref]$null) | select content, type | ft -auto

This dumps out the following information. It's not as rich as the AST parser in v3, but it's still useful:

    Content                   Type
    -------                   ----
    Get-ChildItem          Command
    |                     Operator
    where-object           Command
    -filter       CommandParameter
    {                   GroupStart
    _                     Variable
    .                     Operator
    Length                  Member
    -gt                   Operator
    1000000                 Number
    }                     GroupEnd

Hope this helps.