A few Powershell functions that are helpful to have in psake build scripts. Some have .net in mind and assume a bin folder or NuGet package directory is desired.

helpers.ps1

function Find-PackagePath {
	[CmdletBinding()]
	param(
		[Parameter(Position=0, Mandatory=1)]$packagesPath,
		[Parameter(Position=1, Mandatory=1)]$packageName
	)

	return (Get-ChildItem ($packagesPath + "\" + $packageName + "*")).FullName | Sort-Object $_ | select -Last 1
}

function Prepare-Tests {
	[CmdletBinding()]
	param(
		[Parameter(Position=0, Mandatory=1)]$testRunnerName,
		[Parameter(Position=1, Mandatory=1)]$publishedTestsDirectory,
		[Parameter(Position=2, Mandatory=1)]$testResultsDirectory
	)

	$projects = Get-ChildItem $publishedTestsDirectory -Filter *Tests 

	Write-Host "$($projects.Count) $testRunnerName project(s) have been found:"

	Write-Host ($prjects | Select $_.Name)

	# Create the test results directory if needed
	if(!(Test-Path $testResultsDirectory))
	{
		Write-Host "Creating test results directory located at $testResultsDirectory"
		mkdir $testResultsDirectory | Out-Null
	}

	# Get the list of test DLLs
	$testAssembliesPaths = $projects | ForEach-Object {$_.FullName + "\bin\" + $_.Name + ".dll" }

	$testAssemblies = [string]::Join(" ", $testAssembliesPaths)

	return $testAssemblies
}

function Find-NuGetPackagePaths {
	[CmdletBinding()]
	param(
		[Parameter(Position=0, Mandatory=1)]$repositoriesPath
	)
	Write-Host $(Get-Location)
	if(!(Test-Path $repositoriesPath))
	{
		throw [System.IO.FileNotFoundException] "$repositoriesPath not found."
	}
	
	[xml]$repositoryConfig = Get-Content -Path $repositoriesPath

	return $repositoryConfig.repositories.repository.path
}

function Get-GitCommit {
	$gitLog = git log --oneline -1
	return $gitLog.Split(' ')[0]
}

function Get-GitBranchName {
	return git rev-parse --abbrev-ref HEAD
}

function CopyDirectory($source, $destination, [regex]$exclude="a^", [regex]$include=".", [switch]$Recurse, [switch]$Flatten) {
	if(!(Test-Path $destination))
	{
		mkdir $destination
	}
	$source = Resolve-Path $source
	Get-ChildItem $source -Recurse:$Recurse | ?{ $_.FullName -notmatch $exclude } | ?{ $_.FullName -match $include } `
	| %{
            if($Flatten)
			{
				$newDestination = Join-Path $destination $_.Name
			}
			else
			{
				$newDestination = Join-Path $destination $_.FullName.Substring($source.path.length)
			}
            if($_.PSIsContainer)
            {
                Copy-Item $_.FullName -Destination $newDestination -Force
            }
            else
            {
                New-Item -ItemType File -Path $newDestination -Force
                Copy-Item $_.FullName $newDestination -Force
            }
           
        }
}

function CopyFiles($source, $destination, [regex]$exclude="a^", [regex]$include=".", [switch]$Recurse, [switch]$Flatten) {
	if(!(Test-Path $destination))
	{
		mkdir $destination
	}
	$source = Resolve-Path $source
	Get-ChildItem $source -Recurse:$Recurse | ?{ ! $_.PSIsContainer } | ?{ $_.FullName -notmatch $exclude } | ?{ $_.FullName -match $include } `
	| %{
			if($Flatten)
			{
				$newDestination = Join-Path $destination $_.Name
			}
			else
			{
				$relativePath = $_.FullName.Substring($source.path.length)
				if([string]::IsNullOrEmpty($relativePath))
				{
					#We passed in a file source, we should pass in a file destination
					$newDestination = $destination
				}
				else
				{
					$newDestination = Join-Path $destination $_.FullName.Substring($source.path.length)
				}
			}
            New-Item -ItemType File -Path $newDestination -Force
            Copy-Item $_.FullName $newDestination -Force
        }
}

function ReplaceInFile($source, $oldVal, $newVal) {
	if(!(Test-Path $source))
	{
		return
	}
	Write-Host "Replacing $source"
	$try = 0
	$limit = 3
	while (1)
	{
		$try++
		try 
		{
			#Set-Content $source throws 'Exception: Stream was not readable.' unreliably
			#might switch to %{[System.IO.File]::WriteAllLines($source,$_)} but messes with newlines
			(Get-Content $source) -Replace $oldVal, $newVal | Set-Content $source
			break;
		}
		catch
		{
			if ($try -lt $limit)
			{
				Sleep -Seconds 1
				Write-Host "retrying..." -ForegroundColor Red
			}
			else 
			{
				throw
			}
		}
	} 
}

function EnsureDirExists($path) {
	if(!(Test-Path $path))
	{
		mkdir $path
	}
}

function Remove-Directory($path, [switch]$Recurse, [switch]$Force) {
	Get-ChildItem -Path $path -Recurse:$Recurse -Force:$Force | Where-Object { -not ($_.psiscontainer) } | Remove-Item –Force
	Remove-Item -Recurse:$Recurse -Force:$Force $path
}