Replace tokens in config file with values from environment

Replace-Tokens.ps1

param(
    $SourceFile,
    $TokenStart = '__',
    $TokenEnd = '__'
)

function Get-EnvironmentVariables
{
    $env = @{}

    Get-ChildItem -Path env:* | ForEach-Object {
        $item = $_
        #variable names come out of VSTS with underscores, even though we specify them with dots
        #our config transforms also use dots
        $key = $item.Key -replace '_','.'      
        
        If(-Not $env.ContainsKey($key)) {
            $env.Add($key, $item.Value)
        }        
    }

    return $env
}

function Replace-Tokens 
{
    param(
        $SourceFile,
        $TokenStart,
        $TokenEnd
    )

    $content = Get-Content -Path $SourceFile | ForEach-Object {
        $line = $_
        $TokenTable = Get-EnvironmentVariables
        $TokenTable.GetEnumerator() | ForEach-Object {
            $token = $_
            $key = $TokenStart + $token.Key + $TokenEnd
            # case-insensitive match...
            if ($line -match $key) {
                $line = $line -replace $key, $token.Value
            }
        }
        $line
    }

    Set-Content -Value $content -Path $SourceFile -Force
}

Replace-Tokens -SourceFile $SourceFile -TokenStart $TokenStart -TokenEnd $TokenEnd