How to parse and format a string with placeholders, and only bring in the tokens you want.

Format-[Un]SafeString.ps1

$Make = "Tesla"
$Model = "X"
$Year = 2017
$Format = "`$Year `$Make `$Model"

Function Format-UnsafeString {
  Param(
    [Parameter(Position = 0, Mandatory)]
    [string]$Format
    ,
    [Parameter()]
    [string]$Make = "Ford"
    ,
    [Parameter()]
    [string]$Model = "Mustang"
  )
  Process {
    $ExecutionContext.InvokeCommand.ExpandString($Format)
  }
}

Function Format-SafeString {
  Param(
    [Parameter(Position = 0, Mandatory)]
    [string]$Format
    ,
    [Parameter()]
    [string]$Make = "Ford"
    ,
    [Parameter()]
    [string]$Model = "Mustang"
  )
  Begin {
    $Powershell = [powershell]::Create()
  }
  Process {
    $Powershell = [Powershell]::Create()
    [void]$Powershell.AddScript($scriptBlock)
    [void]$Powershell.AddParameter("_", "`${Make} `${Model}")
    [void]$Powershell.AddParameter("Make", $Make)
    [void]$Powershell.AddParameter("Model", $Model)
    Return $Powershell.Invoke()
  }
  End {
    $Powershell.Dispose()
  }
}

# Will include Year, but we don't want it to
# ExecutionContext is aware of $Year declared above
Format-UnsafeString $Format -Make "Jeep" -Model "Wrangler"

# Will NOT include year (sandboxed)
# ExectionContext is running within the confines of the sandbox
Format-SafeString $Format -Make "Jeep" -Model "Wrangler"