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Yasitha Bogamuwa
Asked: 2019-11-15 08:13:08 +0800 CST

How to use splatting to pass parameters to commands in PowerShell inside DOUBLE QUOTES

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I'm trying to deploy a Windows Service using msdeploy.exe. In here I'm using hashtables to make it clear and readable.

For this example, I use the following variables

$WIN_SERVICE_NAME="myService"
$SERVICE_APP_FILE="C:\Users\My User\Desktop\myService.exe"

# Hashtable for the windows service

$params = @{
   Name = "$WIN_SERVICE_NAME"
   BinaryPathName = "$SERVICE_APP_FILE"
   StartupType = "Automatic"
   Description = "Release Management Service"
}

In order to make sure I can get correct values using the splatting operator, I used the following command and it returns expected output.

Command: Write-Host @params

Output: -DisplayName: myService -StartupType: Automatic -Description: Release Management Service -Name: myService -BinaryPathName: C:\Users\My User\Desktop\myService.exe

But, when I try to use splatting operator inside double quotes like this:

Write-Host "@params"

It returns @params as the output without expanding it.

In summary, that's the same thing happening inside my function. I'm using double quotes and splatting operator could not expand.

# Deploying windows service using msdeploy.exe

& "C:\Program Files\IIS\Microsoft Web Deploy V3\msdeploy.exe" `
   -- AVOIDING UNNECESSARY LINES--
   -postSync:runCommand="`"powershell if (Get-Service $WIN_SERVICE_NAME -ErrorAction SilentlyContinue){ sc.exe delete $WIN_SERVICE_NAME; New-Service @params; Start-Service $WIN_SERVICE_NAME } else { New-Service @params; Start-Service $WIN_SERVICE_NAME }`""

Could you please help me to fix this issue? I want to expand the splatting operator inside double quotes or need another solution without adding all parameters in a single line. Thanks in advance!

windows

2 Answers

  1. You can't pre-expand a splat variable inside a string. It's directly interpreted by the PowerShell command parser.

    Also, the command you are sending to msdeploy is ultimately starting its own PowerShell session. So if you want to use a variable (such as a splat variable), it has to be defined within the code you've written for that session.

    So you'd have to add the $params = @{<blah>} code within that runCommand string. So something like this:

    & "C:\Program Files\IIS\Microsoft Web Deploy V3\msdeploy.exe" `
   -- AVOIDING UNNECESSARY LINES--
   -postSync:runCommand="`"powershell $params = @{Name=`"$WIN_SERVICE_NAME`";StartupType=`"Automatic`"}; if (Get-Service $WIN_SERVICE_NAME -ErrorAction SilentlyContinue){ sc.exe delete $WIN_SERVICE_NAME; New-Service @params; Start-Service $WIN_SERVICE_NAME } else { New-Service @params; Start-Service $WIN_SERVICE_NAME }`""

    Notice the escaped quotes in the hashtable declaration. You need this because your current PowerShell session will expand the variables like $WIN_SERVICE_NAME in the string you're creating. But you still need quotes around the value for the future PowerShell session that will actually be running the code in the command.

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  2. Rather than using a splat in this case, I suggest just putting the parameters in a single string variable. If you really want to use a slat for clarity or reasons, then make a string variable populated by the splat.

    For example:

    $params = @{
   Name = "service name"
   BinaryPathName = "C:\Program Files\Some Service\"
   StartupType = "Automatic"
   Description = "Release Management Service"
}
$newparams = ""
$newparams += foreach($k in $params.Keys) {
    Write-Output "-$k `"$($params.Item($k))`""
    }
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