C#•13mo ago

How do you get the output type from a powershell script with System.Management.Automation?

I am trying to figure out how to get the type specified in a powershell script [OutputType([int])] for example. I can find it in the parsed attributes but it's just treated as an attribute that has "[int]", so it's not seen as a type but just the string value. But there seems to be a OutputTypeAttribute class, but i can't find any information on how to get a hold of that.

13 Replies

Jothay•13mo ago

If you are referring to reading this from C#:

var attr = instance.GetType()
    .GetProperty("MyProp")
    .GetCustomAttributes<OutputTypeAttribute>()
    .SingleOrDefault()
var val = attr.Value;

var attr = instance.GetType()
    .GetProperty("MyProp")
    .GetCustomAttributes<OutputTypeAttribute>()
    .SingleOrDefault()
var val = attr.Value;

That should get you the idea of how to get it

jcotton42•13mo ago

@fjarilsmannen are you like looking at the syntax tree?

function Send-Greeting
{
  [CmdletBinding()]
  [OutputType([String])]
  Param ($Name)

  "Hello, $Name"
}

> $f = ${Function:Send-Greeting}
> $f.Ast.Body.ParamBlock.Attributes[1].PositionalArguments

TypeName StaticType  Extent   Parent
-------- ----------  ------   ------
String   System.Type [String] [OutputType([String])]

function Send-Greeting
{
  [CmdletBinding()]
  [OutputType([String])]
  Param ($Name)

  "Hello, $Name"
}

> $f = ${Function:Send-Greeting}
> $f.Ast.Body.ParamBlock.Attributes[1].PositionalArguments

TypeName StaticType  Extent   Parent
-------- ----------  ------   ------
String   System.Type [String] [OutputType([String])]

$f is a ScriptBlock

Fjärilsmannen•13mo ago

@jothay Not sure what the property is here? @jcotton42 That's basically how i find it right now, though it's not a function but the script itself. But as you can see it doesn't show the proper type, it's seen as System.Type and TypeName is simply just the text it shows, so it will show whatever you write and doesn't indicate the actual type here it seems.

jcotton42•13mo ago

well yeah, it's just the syntax tree if you want an actual System.Type instance, use something like Type.GetType(string typeNam) though, be aware it won't necessarily be a "real" type

Jothay•13mo ago

For common stuff like that, you could switch case the type values and handle string, int, etc individually

jcotton42•13mo ago

as OutputType allows strings in addition to type literals

Fjärilsmannen•13mo ago

jcotton42•13mo ago

it's not uncommon to use a "fake" typename in custom powershell objects to allow for things like formatting rules to apply automatically

Fjärilsmannen•13mo ago

hmm, is there some better way to se the output type? It's meant to be read from C# and i'm in control of the scripts, so just having a way to set a real type that can be read would be best. The same way you can with normal parameters. For example a dummy variable perhaps, not sure if those can be read though.

jcotton42•13mo ago

I mean parsing from the AST is likely your best bet I don't think PowerShell has a public semantic model like C# does

Fjärilsmannen•13mo ago

ah okay. How do i actually get TypeName from an ExpressionAst, i can see it when printing the whole object, but i can't access that property

jcotton42•13mo ago

b/c it's actually TypeExpressionAst you need to cast it or do an is check

Fjärilsmannen•13mo ago

Ah, got it, thanks:)!

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How do you get the output type from a powershell script with System.Management.Automation?