Passing parameters to -EncodedCommand

When invoking PowerShell from cmd/bat files -EncodedCommand is a great way to pass the actual PowerShell code to powershell.exe without worrying about escaping various special characters. This allows you to have just a single batch file (with no external PowerShell scripts whatsoever) which has PowerShell code right inside the file which looks something like:

powershell.exe -EncodedCommand DQAKAA0ACgAJACQAcABhAHIAYQBtAHMAIAA9ACAARwBlAHQALQBDAG8AbgB0AGUAbgB0ACAAJABlAG4AdgA6AFQARQBNAFAAXABwAGEAcgBhAG0AcwAuAHQAeAB0AA0ACgAJACIAUwBlAGUAIAB3AGgAaQBjAGgAIABwAGEAcgBhAG0AZQB0AGUAcgBzACAAUABvAHcAZQByAFMAaABlAGwAbAAgAGcAbwB0ADoAIAAkAHAAYQByAGEAbQBzACIADQAKAAkADQAKAA==

What I was recently pointed to, is that this approach has one limitation: how do you pass parameters to this PowerShell code? For example, say, cmd file gets parameters from command-line and wants to pass them to PowerShell – you obviously don’t know the values in advance so you cannot pre-encode them.

The easiest way that I found is: simply put the value from cmd file to a temporary file, and then read the file from PowerShell code.

So, for illustration purpose, my super-advanced PowerShell script will simply output the parameters:

    $params = Get-Content $env:TEMP\params.txt
    "See which parameters PowerShell got: $params"

As you can see, I am getting the parameters by reading the content of pre-defined file in %TEMP% location.

Now, let’s encode this by running:

$code = {

    $params = Get-Content $env:TEMP\params.txt
    "See which parameters PowerShell got: $params"
    
}

[convert]::ToBase64String([Text.Encoding]::Unicode.GetBytes($code))

In my case I got:

DQAKAA0ACgAJACQAcABhAHIAYQBtAHMAIAA9ACAARwBlAHQALQBDAG8AbgB0AGUAbgB0ACAAJABlAG4AdgA6AFQARQBNAFAAXABwAGEAcgBhAG0AcwAuAHQAeAB0AA0ACgAJACIAUwBlAGUAIAB3AGgAaQBjAGgAIABwAGEAcgBhAG0AZQB0AGUAcgBzACAAUABvAHcAZQByAFMAaABlAGwAbAAgAGcAbwB0ADoAIAAkAHAAYQByAGEAbQBzACIADQAKAAkADQAKAA==

Now we are ready to put this into cmd:

echo %* > %TEMP%\params.txt

Basically, all I do is write the command-line arguments which the batch file got to a temporary file, and then invoke our PowerShell script.

And here’s the proof that this actually works:

c:\Scripts>pass-params.cmd Here are my parameters!


c:\Scripts>echo Here are my parameters!  1>C:\Users\dsotniko\AppData\Local\Temp\

params.txt
c:\Scripts>powershell.exe -EncodedCommand  DQAKAA0ACgAJACQAcABhAHIAYQBtAHMAIAA9A

CAARwBlAHQALQBDAG8AbgB0AGUAbgB0ACAAJABlAG4AdgA6AFQARQBNAFAAXABwAGEAcgBhAG0AcwAuA

HQAeAB0AA0ACgAJACIAUwBlAGUAIAB3AGgAaQBjAGgAIABwAGEAcgBhAG0AZQB0AGUAcgBzACAAUABvA

HcAZQByAFMAaABlAGwAbAAgAGcAbwB0ADoAIAAkAHAAYQByAGEAbQBzACIADQAKAAkADQAKAA==

See which parameters PowerShell got: Here are my parameters!

Now you can have a single batch file, encapsulating PowerShell code and capable of passing parameters to it!

5 Responses to “Passing parameters to -EncodedCommand”

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1 Rich Beckett July 7, 2011 at 9:38 pm

That was very interesting, helpful and instructive. I believe I saw a post recently regarding active Roles server where someone wanted to do exactly this, pass arguments which included curly braces. I now have amuch better understanding of some of the finer aspects of PowerShell

Thanks.

2 Anonymous July 2, 2013 at 12:36 am

Or you could look at it the other way and facepalm. Why is it so hard to escape characters in Powershell? And why is Windows *so* bad at validating input and guarding against attacks?

3 John Hofmann November 10, 2017 at 1:21 pm

I know this isn’t exactly timely, but while researching this problem, I found your blog, and thought I’d share the method I came up with to do this without the need to create any extra files.

You can simply set the variables in your batch script:

SET “VARIABLE1=TEXT”

You can then account for the variables ahead of time in your PowerShell script before encoding it:

If ($env:VARIABLE1) {Write-Output $env:VARIABLE1}

- 4 Lee Fitzsimmons November 13, 2017 at 6:43 am
  
  Here’s another variation I just finished so thought I share as well – pipe the parameters via echo eg:
  
  echo -p1 this -p2 is -p3 a -p4 test | powershell.exe -encodedcommand “thebase64encodedscript”
  
  Then at the top of your encoded powershell script, something like the following to read in your parameters.
  
  $params = @{}
  $curparam = “”
  
  $pr = [Console]::In.ReadLine()
  $pr = $pr -replace ‘\s+$’, ”
  $a = $pr | Select-String -Pattern ‘(?:^| )(\”(?:[^\”]+|\”\”)*\”|[^ ]*)’ -AllMatches
  
  foreach($x in $a.Matches) {
  
  $n = $($x -replace ‘^\s+’, ”) -replace ‘\s+$’, ”
  if($n -match (‘\-[0-9A-z]+’)) {
  $curparam = $n
  } else {
  if(-not [string]::IsNullOrEmpty($curparam)) {
  $params.add($curparam , $n)
  }
  }
  }
  
  write-host $params.’-p1′
  
  Your parameters are then accessible via the arraylist $params.
  Credit for the regex goes to jimplode: https://stackoverflow.com/questions/3776458/split-a-comma-separated-string-with-both-quoted-and-unquoted-strings
  
  in answer to anon , the specific use case for this is that in SCCM, powershell scripts in task sequences must be taken from a package. SCCM does however provide a way to execute a regular command, so being able to wrap the powershell script this way circumvents the need to create a package for simple one off scripts.
  
  - 5 Lee Fitzsimmons November 13, 2017 at 6:49 am
    
    Note that the above only works when executed from cmd, not a powershell prompt. In powershell, in.readline will take each space-separated item echoed as a separate line. the code can be easily modified for this scenario