The definitive way to use PowerShell from an msbuild script

Test.csproj

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <!-- #1 Place this line at the top of any msbuild script (ie, csproj, etc) -->
  <PropertyGroup><PowerShell># 2>nul || type %~df0|find /v "setlocal"|find /v "errorlevel"|powershell.exe -noninteractive -&amp; exit %errorlevel% || #</PowerShell></PropertyGroup>
 
  <!-- #2 in any target you want to run a script -->
  <Target Name="default" >

    <PropertyGroup> <!-- #3 prefix your powershell script with the $(PowerShell) variable, then code as normal! -->
      <myscript>$(PowerShell)
      #
      # powershell script can do whatever you need.
      #
      dir ".\*.cs" -recurse |% {
        write-host Examining file named:  $_.FullName
        # do other stuff here...
      } 
      $answer = 2+5
      write-host Answer is $answer !
      </myscript>
    </PropertyGroup>
  
    <!-- #4 and execute the script like this -->
    <Exec Command="$(myscript)" EchoOff="true" /> 
    
    <!-- 
    Notes:
    ======
    - You can still use the standard Exec Task features! (see: https://msdn.microsoft.com/en-us/library/x8zx72cd.aspx)
    - if your powershell script needs to use < > or & characters, just place the contents in a CDATA wrapper:
    
        <script2><![CDATA[  $(PowerShell)
          # your powershell code goes here!
          write-host "<<Hi mom!>>"
        ]]></script2>
    
    - if you want return items to the msbuild script you can get them:
        
        <script3>$(PowerShell)
          # your powershell code goes here!
          (dir "*.cs" -recurse).FullName
        </script3>
    
        <Exec Command="$(script3)" EchoOff="true" ConsoleToMSBuild="true"> 
            <Output TaskParameter="ConsoleOutput" PropertyName="items" />
        </Exec>

        <Touch Files="$(items)" /> <- see! then you can use those items with another msbuild Task
    
    -->

  </Target>
</Project>

This is great - do you know how to reference other variables from within the script? For example, accessing the MyNumber property from within the script:

<PropertyGroup>
    <MyNumber>2</MyNumber>
</PropertyGroup>
<PropertyGroup> <!-- #3 prefix your powershell script with the $(PowerShell) variable, then code as normal! -->
    <myscript>$(PowerShell)
         .....
         $x = 2
         If ($x -eq $MyNumber) {
              .....
         }
         .....        
    </myscript>
</PropertyGroup>

did you try $(MyNumber) ? IIRC that should work

I found this to be extremely helpful ! However, I ran through some limitations with the PowerShell command. Those limitations are:

1. It fails if the PowerShell script is inlined in the Exec task. e.g. <Exec Command="$(PowerShell)" Write-Host &quot;ok&quot;" />
2. The actual return code of PowerShell is not returned. This is a limitation of the Windows Command Line. With the & exit %errorlevel% on the same line as the PowerShell command, 0 is always returned even if Exit -1 is in the PowerShell script. In order for the PowerShell process return code to be returned to Visual Studio, the exit %errorlevel% must be on a separate line.
3. It fails if the PowerShell script declared in the property ends with last powershell command ]] (where ]] are the closing braces of the ![CDATA[ tag on the same line as the last PowerShell command).
4. If the PowerShell script is a function ending with a call to that function and that function has required parameters, the PowerShell command fails if an explicit %0D%0A is not added at the end of the command. e.g. <Exec Command="$(PowerShell) $(ScriptWithFunctionRequiringParameters) &quot;@(ItemGroupUsedAsParameter)&quot; %0D%0A" />

Now, that being said, I used your scheme and changed the find /v commands with PowerShell -replace commands which allow using regular expressions. What I came up with is:

<PropertyGroup>
  <PowerShellCommand>
    powershell.exe -Command "&amp;{((Get-Content \"%~df0\" -Raw) -replace \"(?sm).*:START_POWERSHELL_SCRIPT\", \"\" -replace \"exit %%.*%%\", \"\") + \"`n\"}"|powershell.exe -ExecutionPolicy Bypass -NoLogo -NonInteractive -NoProfile -
    exit %ERRORLEVEL%
    :START_POWERSHELL_SCRIPT
    %0D%0A
  </PowerShellCommand>
</PropertyGroup>

With this improved PowerShell command, I was able to fix all the limitations previously mentioned, I thought I'd share it with you since the original command found here really helped be grasp how MsBuild was actually calling PowerShell.

  <Target Name="Trigger" AfterTargets="Generate" >
    <PropertyGroup>
      <PowerShellCommand Condition=" '$(OS)' == 'Windows_NT' " >powershell</PowerShellCommand>
      <PowerShellCommand Condition=" '$(OS)' == 'Unix' " >pwsh</PowerShellCommand>
      <ClientGenTriggerScript>$(MSBuildProjectDirectory)\..\..\..\.build\client_gen.ps1</ClientGenTriggerScript>
    </PropertyGroup>
    <Exec Command="$(PowerShellCommand) -ExecutionPolicy Unrestricted -NoProfile -File $(ClientGenTriggerScript) -parameter1 p1 -parameter2 $(p2) --Verbose" />
  </Target>

I use it this way.