One of the natural languages to explore after learning PowerShell is C#. It uses many of the same programming techniques as PowerShell and uses the same classes and methods in the .NET Framework as PowerShell does, too. In addition, C# sometimes offers language features or performance benefits not available through PowerShell.
Rather than having to move to C# completely for these situations, Example 158 lets you write and invoke C# directly in your script.
Example 158. InvokeInline.ps1
################################################################################
## InvokeInline.ps1
## Library support for inline C#
##
## Usage
## 1) Define just the body of a C# method, and store it in a string. "Here
## strings" work great for this. The code can be simple:
##
## $codeToRun = "Console.WriteLine(Math.Sqrt(337));"
##
## or more complex:
##
## $codeToRun = @"
## string firstArg = (string) ((System.Collections.ArrayList) arg)[0];
## int secondArg = (int) ((System.Collections.ArrayList) arg)[1];
##
## Console.WriteLine("Hello {0} {1}", firstArg, secondArg );
##
## returnValue = secondArg * 3;
## "@
##
## 2) (Optionally) Pack any arguments to your function into a single object.
## This single object should be stronglytyped, so that PowerShell does
## not treat it as a PsObject.
## An ArrayList works great for multiple elements. If you have only one
## argument, you can pass it directly.
##
## [System.Collections.ArrayList] $arguments =
## NewObject System.Collections.ArrayList
## [void] $arguments.Add("World")
## [void] $arguments.Add(337)
##
## 3) Invoke the inline code, optionally retrieving the return value. You can
## set the return value in your inline code by assigning it to the
## "returnValue" variable as shown above.
##
## $result = InvokeInline $codeToRun $arguments
##
##
## If your code is simple enough, you can even do this entirely inline:
##
## InvokeInline "Console.WriteLine(Math.Pow(337,2));"
##
################################################################################
param( [string] $code = $(throw "Please specify the code to invoke"), [object] $arg, [string[]] $reference = @() )
## Stores a cache of generated inline objects. If this library is dotsourced ## from a script, these objects go away when the script exits.
Example 158. InvokeInline.ps1 (continued)
if(not (TestPath Variable:\Lee.Holmes.inlineCache)) { ${GLOBAL:Lee.Holmes.inlineCache} = @{} }
## The main function to execute inline C#. ## Pass the argument to the function as a stronglytyped variable. They will ## be available from C# code as the Object variable, "arg". ## Any values assigned to the "returnValue" object by the C# code will be ## returned to the caller as a return value.
function main
{ ## See if the code has already been compiled and cached $cachedObject = ${Lee.Holmes.inlineCache}[$code]
## The code has not been compiled or cached if($cachedObject eq $null) {
$codeToCompile = @" using System;
public class InlineRunner
{ public Object Invoke(Object arg) {
Object returnValue = null;
$code
return returnValue; } } "@
## Obtains an ICodeCompiler from a CodeDomProvider class. $provider = NewObject Microsoft.CSharp.CSharpCodeProvider
## Get the location for System.Management.Automation DLL $dllName = [PsObject].Assembly.Location
## Configure the compiler parameters $compilerParameters = NewObject System.CodeDom.Compiler.CompilerParameters
$assemblies = @("System.dll", $dllName) $compilerParameters.ReferencedAssemblies.AddRange($assemblies) $compilerParameters.ReferencedAssemblies.AddRange($reference) $compilerParameters.IncludeDebugInformation = $true $compilerParameters.GenerateInMemory = $true
## Invokes compilation.
Example 158. InvokeInline.ps1 (continued)
$compilerResults = $provider.CompileAssemblyFromSource($compilerParameters, $codeToCompile)
## Write any errors if generated. if($compilerResults.Errors.Count gt 0) {
$errorLines = "`n$codeToCompile" foreach($error in $compilerResults.Errors) {
$errorLines += "`n`t" + $error.Line + ":`t" + $error.ErrorText } WriteError $errorLines
} ## There were no errors. Store the resulting object in the object " ## cache. else {
${Lee.Holmes.inlineCache}[$code] = $compilerResults.CompiledAssembly.CreateInstance("InlineRunner") }
$cachedObject = ${Lee.Holmes.inlineCache}[$code] }
## Finally invoke the C# code if($cachedObject ne $null) {
return $cachedObject.Invoke($arg) } }
. Main
