Why is my PowerShell function's parameter showing up as empty/blank?

Question

On a whim, in order to learn PowerShell, which I know I'm woefully behind on, I decided to write a super simple script to use MSBuild to clean a bunch of solutions in code, then build them with a certain set of arguments. Here's the script:

$sourceDir = Split-Path -Path $MyInvocation.MyCommand.Definition -Parent
$cleanArgs = '/t:clean /verbosity:q /nologo /P:Configuration=Debug'
$buildArgs = '/verbosity:q /nologo /P:Platform="Any CPU";Configuration=Debug'
$solutions = @("asdf.sln","qwer.sln","zxcv.sln","yuio.sln","hjkl.sln","nm.sln")

function buildWithArgs([string[]]$solutionsToBuild = @(), [string]$args = 'default')
{
    Write-Host args: $args
    foreach($sln in $solutionsToBuild)
    {
        & $env:WINDIR\Microsoft.NET\Framework64\v4.0.30319\msbuild.exe "$sourceDir\$sln $args" | Out-Default
    }
}

buildWithArgs $solutions $buildArgs
buildWithArgs $solutions $cleanArgs

Now, my problem is that the function "buildWithArgs" doesn't respect the $args parameter, which is always empty when I run or debug the script, no matter what I pass in. The $solutionsToBuild parameter works flawlessly, however. Do I have improper syntax? Even if it were the case that my $cleanArgs string was somehow improperly formatted or not escaped, I can't even make the function work with simple strings like "asdf", as $args is always empty when I run it. Thanks for any help you can provide to what is assuredly some small, silly error!

Things I have tried: surrounding MSBuild's args with quotes, changing $cleanArgs' quotes from double (with escaping around "Any CPU") to single quotes, changing the '&' command to Invoke-Item and Invoke-Expression. I should note that if I refer to the global variables $cleanArgs or $buildArgs, instead of a function parameter, it works flawlessly. — RJ Cantrell
– RJ Cantrell, Commented Sep 11, 2012 at 18:18

Aaron Jensen · Accepted Answer · 2012-09-11 18:34:07Z

First, $args is a special, built-in parameter in PowerShell, which represents all the arguments to a function. One of the side-effects to this is you can't see its value in the ISE debugger. Try changing its name to MSBuildArgs.

Make sure you define, buildArgs and cleanArgs as arrays. You're defining them as one single string. You do this so you can use PowerShell's splat operator (@ instead of $ when referencing a variable), which sends each argument in an array as a parameter to a command.

Lastly, you don't need to quote parameters that are stored in variables. PowerShell will do any quoting for you.

After making these changes, you'll have something like this:

$sourceDir = Split-Path -Path $MyInvocation.MyCommand.Definition -Parent
$cleanArgs = @('/t:clean','/verbosity:q','/nologo','/P:Configuration=Debug')
$buildArgs = @('/verbosity:q','/nologo','/P:Platform="Any CPU";Configuration=Debug')
$solutions = @("asdf.sln","qwer.sln","zxcv.sln","yuio.sln","hjkl.sln","nm.sln")

function buildWithArgs([string[]]$solutionsToBuild = @(), [string[]]$MSBuildArgs= 'default')
{
    Write-Host args: $args
    foreach($sln in $solutionsToBuild)
    {
        $msbuildPath = Join-Path $env:WINDIR Microsoft.NET\Framework64\v4.0.30319\msbuild.exe -Resolve
        & $msbuildPath (Join-Path $sourceDir $sln -Resolve) @MSBuildArgs | `
            Out-Default
    }
}

buildWithArgs $solutions $buildArgs
buildWithArgs $solutions $cleanArgs

Mostly correct! unfortunately, the parameter including the space ('/P:Platform="Any CPU";Configuration=Debug') causes MSBuild to explode, as it thinks that the text after the space is a new parameter. Sad! But I can try to figure that out...

latkin · Accepted Answer · 2012-09-11 18:25:21Z

$args is a special automatic variable in powershell functions. It contains an array of parameters which are not otherwise bound to the declared parameters of the function. By plain bad luck/inexperience, you happened to name one of your declared parameters the same, which will cause issues.

If you rename your parameter to something else, say $BuildArgs, it should be properly bound.

Note, however, that your current code will execute msbuild with a single parameter consisting of the solution path and args together. It is not the syntax to invoke msbuild with multiple arguments. If this causes issues for you I would suggest opening another question or searching online for that particular issue, just so this question does not get too big.

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