Archive for July 6th, 2011

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

powershell.exe -EncodedCommand DQAKAA0ACgAJACQAcABhAHIAYQBtAHMAIAA9ACAARwBlAHQALQBDAG8AbgB0AGUAbgB0ACAAJABlAG4AdgA6AFQARQBNAFAAXABwAGEAcgBhAG0AcwAuAHQAeAB0AA0ACgAJACIAUwBlAGUAIAB3AGgAaQBjAGgAIABwAGEAcgBhAG0AZQB0AGUAcgBzACAAUABvAHcAZQByAFMAaABlAGwAbAAgAGcAbwB0ADoAIAAkAHAAYQByAGEAbQBzACIADQAKAAkADQAKAA==

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!


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© 2007-2014 Dmitry Sotnikov

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